Add integration test for OffSetters method

[Cliabhach]

Right now the tests in OffsetImageViewTest.java don't verify correct appearance of the ImageView post-offsetting. Find a way to compare the result of calling this method with some sort of pre-computed bitmap.

Note that this will be probably be the biggest beneficiary upon completion of issue #19

[Cliabhach]

Note that the low-level android drawing code is not accessible to unit tests, so this must be an integration test.