TIMOB-13392: Android scrollable tabs

Android tab group can now by default be navigated by swipes (e.g. see Play Store app). The functionality can be toggled with the new `TabGroup.swipeable` property. In addition, tab navigation can be disabled (or re-enabled) by calling `disableTabNavigation(boolean)`. Plus added tab `selected` and `unselected` events (currently these events exist in Android only. In iOS the tab focus/blur events do the same - I suggest they be renamed to selected/unselected). Note that all additional events are fired exactly as before.
The logic here is not correct. That's why I suggested to add it to the list of propertyAccessors.
No matter the view is ready or not, tabgroupProxy.swipeable should always return the value that the user had set, which is "swipeTabs" before the view is ready and "tabGroup.swipeable" after the view is ready.
If you use propertyAccessor, you don't need to worry about this logic at all. Please use propertyAccessor and set the default value like https://github.com/appcelerator/titanium_mobile/blob/master/android/titanium/src/java/org/appcelerator/titanium/proxy/TiViewProxy.java#L111 . Then you can remove the set/getSwipeable methods here. When you need the value of this property, you can use 
TiConvert.toBoolean(tabgroupProxy.getProperty("swipeable"), true)