Replace pull-to-refresh code with Chris Bane's Android-PullToRefresh lib

This library is under active development and uses Maven, making it easier
for me as a potential contributor to get it building. It's also packaged
as an apklib making it easier to use without having to copy and paste code
into my own project.

Note that it was necessary to change the view's id from "@android:id/list"
to "@+id/pull_to_refresh_list_wrapper" to avoid this fatal error on screen
rotation:

E/AndroidRuntime(31031): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.madgag.agit/com.madgag.agit.BranchViewer}: java.lang.IllegalArgumentException: Wrong state class, expecting View State but received class android.widget.AbsListView$SavedState instead. This usually happens when two views of different type have the same id in the same hierarchy. This view's id is id/list. Make sure other views do not use the same id.
E/AndroidRuntime(31031): 	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
E/AndroidRuntime(31031): 	at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
E/AndroidRuntime(31031): 	at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3351)
E/AndroidRuntime(31031): 	at android.app.ActivityThread.access$700(ActivityThread.java:123)
E/AndroidRuntime(31031): 	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1151)
E/AndroidRuntime(31031): 	at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(31031): 	at android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(31031): 	at android.app.ActivityThread.main(ActivityThread.java:4424)
E/AndroidRuntime(31031): 	at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(31031): 	at java.lang.reflect.Method.invoke(Method.java:511)
E/AndroidRuntime(31031): 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
E/AndroidRuntime(31031): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
E/AndroidRuntime(31031): 	at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime(31031): Caused by: java.lang.IllegalArgumentException: Wrong state class, expecting View State but received class android.widget.AbsListView$SavedState instead. This usually happens when two views of different type have the same id in the same hierarchy. This view's id is id/list. Make sure other views do not use the same id.
E/AndroidRuntime(31031): 	at android.view.View.onRestoreInstanceState(View.java:9963)
E/AndroidRuntime(31031): 	at com.handmark.pulltorefresh.library.PullToRefreshBase.onRestoreInstanceState(PullToRefreshBase.java:708)
E/AndroidRuntime(31031): 	at android.view.View.dispatchRestoreInstanceState(View.java:9939)
E/AndroidRuntime(31031): 	at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2318)
E/AndroidRuntime(31031): 	at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2324)
E/AndroidRuntime(31031): 	at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2324)
E/AndroidRuntime(31031): 	at android.view.View.restoreHierarchyState(View.java:9917)
E/AndroidRuntime(31031): 	at com.android.internal.policy.impl.PhoneWindow.restoreHierarchyState(PhoneWindow.java:1600)
E/AndroidRuntime(31031): 	at android.app.Activity.onRestoreInstanceState(Activity.java:906)
E/AndroidRuntime(31031): 	at android.app.Activity.performRestoreInstanceState(Activity.java:878)
E/AndroidRuntime(31031): 	at android.app.Instrumentation.callActivityOnRestoreInstanceState(Instrumentation.java:1100)
E/AndroidRuntime(31031): 	at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1934)
E/AndroidRuntime(31031): 	... 12 more
W/ActivityManager(27872):   Force finishing activity com.madgag.agit/.BranchViewer
Fix crash in Clone launcher when user enters just '.git' for the repo url

URIish should probably blow up when some tries to create it with '.git'...!

java.lang.ArrayIndexOutOfBoundsException
at org.eclipse.jgit.transport.URIish.getHumanishName(URIish.java:569)
at com.madgag.agit.CloneLauncherActivity.defaultRepoDirFor(CloneLauncherActivity.java:291)
at com.madgag.agit.CloneLauncherActivity.updateUIWithValidation(CloneLauncherActivity.java:140)
at com.madgag.agit.CloneLauncherActivity$2.afterTextChanged(CloneLauncherActivity.java:98)
at android.widget.TextView.sendAfterTextChanged(TextView.java:6705)
at android.widget.TextView$ChangeWatcher.afterTextChanged(TextView.java:6894)
at android.text.SpannableStringBuilder.sendTextHasChanged(SpannableStringBuilder.java:921)
at android.text.SpannableStringBuilder.change(SpannableStringBuilder.java:401)
at android.text.SpannableStringBuilder.change(SpannableStringBuilder.java:269)
at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:432)
at android.text.SpannableStringBuilder.delete(SpannableStringBuilder.java:218)
at android.text.SpannableStringBuilder.delete(SpannableStringBuilder.java:28)
at android.view.inputmethod.BaseInputConnection.deleteSurroundingText(BaseInputConnection.java:224)
at com.android.internal.view.IInputConnectionWrapper.executeMessage(IInputConnectionWrapper.java:377)
at com.android.internal.view.IInputConnectionWrapper$MyHandler.handleMessage(IInputConnectionWrapper.java:79)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:130)
at android.app.ActivityThread.main(ActivityThread.java:3691)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:907)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:665)
at dalvik.system.NativeStart.main(Native Method)
Warn user if there's not enough room when planning a clone

Thanks to José who worked out that his sdcard being full was the reason
Agit was gnomically failing...

The 128 KB space requirement comes from an quick look at the amount of
space a blank repo takes on an Ubuntu laptop - it probably takes a little
less on an Android device.

$ du -h
40K	./.git/hooks
8.0K	./.git/info
4.0K	./.git/objects/pack
4.0K	./.git/objects/info
12K	./.git/objects
4.0K	./.git/refs/heads
4.0K	./.git/refs/tags
12K	./.git/refs
4.0K	./.git/branches
92K	./.git
96K	.
No longer die if the default repos dir is no longer available

Users can now save to different locations, so it's certainly not a fatal
error.