Refactored MavenCentral interface

Renamed the MavenCentral interface to DependencyResolver (which is a more
accurate description of its purpose) and renamed its implementing classes to
MavenResolver and CachedMavenResolver.
Added ability to run Robolectric tests offline

Set the following system properties to activate the behavior:
  robolectric.offline=true
  robolectric.dependency.dir=<path>

Runtime dependencies will be retrieved from the specified path
instead of being downloaded from Maven.
Further renaming for consistency
Removed RobolectricTestRunner from DependencyResolver methods

Moved the configureMaven() method from RobolectricTestRunner to
MavenDependencyResolver, since it is only applicable there. This
means that DependencyResolver methods no longer require an
instance of RobolectricTestRunner.

THIS IS AN API-BREAKING CHANGE.

Instead of sub-classing RobolectricTestRunner to provide custom
Maven configuration, it is now necessary to subclass
MavenDependencyResolver.
Fix test method names, introduced in 53aa0e480401a10d5d67b8d35bcf900497c4a09c.
Merge pull request #1193 from erichaugh/fixToastTestNames

Fix test method names in ToastTest.
Throw an exception when creating bitmaps with invalid dimensions.

Closes #1197.
Implement ShadowView.getOnCreateContextMenuListener.

Fixes #1194. Closes #1195.
Merge pull request #1189 from awrichar/offline

Added ability to run Robolectric tests offline.
Adding support to partial matching in ShadowIntentFilter.

This patch also fixed the issue with broadcast intents being
delivered solely based on the receiver action. This patch
also filters based on the data type as per spec.

Closes #1162.
Implement ShadowPopupWindow.showAtLocation.

Closes #1200.
Basic activity-alias support.

Closes #1209.