Restore unit tests

[evanp]

When we moved to Gradle, the unit tests disappeared. We need to add them back into the project so we can make changes; this is especially important for testing that updates to the Dropbox API work.

[dae3]

Working on this one now

[dae3]

OK, unit tests are back and running at dae3/todo.txt-android@8758910ceea96c1a3a28f4e10f76bbad2e5ea532.

A number are failing because of test environment problems, mostly seems to be missing mocks for Android system bits.

I'll start working through but it'd be good to get some more eyes on this.

[dae3]

Here's what needs work:

• [x] Mock Environment.getExternalStorageDirectory in DropboxFileUploaderTest
• [x] TodoApplicationTest is failing trying to call setUp on the superclass (ApplicationTestCase)
• [x] DropboxFileDownloaderTest: JUnit is looking for a TestCase(String) or TestCase() constructor
• [x] PhoneNumberParserTest failing the test_withGerman tests; looks like a genuine test failure
• [x] TestBagImplTest is trying to call getContext() on AndroidTestCase
• [x] RelativeDateTest is trying to call runTest on InstrumentationTestCase
• [x] TodoTxtTouchTest, JUnit's not running any of the tests "No tests found in com.todotxt.todotxttouch.test.TodoTxtTouchTest"

Turns out they all just needed to be run by the instrumented test runner. All tests now run, although some still fail, but appear to be genuine failures.

If anyone has a the output of a test run from the pre-Gradle build that'd be great too, to distinguish between genuine test failures and test environment breakage.