R4E UI JUnit improvements

- Introduce an R4EAssert class that wraps JUnit's Assert
- Add an identifying message to the assert statements
- Make some rogue internal test methods 'private'
- Add some comments in test cases
- Re-organize the TestUtils class in logical sections
- Ensure that the projects and the shared data are effectively
  cleared at the start of each test suite (cleanup leftovers)

Notes:

- This is just preliminary work for bug
https://bugs.eclipse.org/bugs/show_bug.cgi?id=399549

- R4EAssert introduces a delay on each call to assertXXX. There is room
for optimization there. On the other hand, the extra delay seemed to
stabilize the tests on my machine...

- Reviewers: pay special attention on the construction of the R4EAssert
objects: the String parameter should match the method name otherwise it
could be very misleading.

- Fixed a bunch of anomalies.

Change-Id: I41b55f7f07337e6d57690970bf9c14c2984f9a8b
18 files changed