Introduce GUI testing

[gyorb]

automatic GUI tests would be nice again if possible for multiple eclipse versions

[dkrupp]

Implement first a simple test sequence, testing the most basic use case.
Prerequisite: We have hello world C project in eclipse.
0. Empty codechecker config (global and local)

1. Add nature. Error message appears that codechecker needs to be configured.
2. Codechecker configuration is given.
3. build is called for hello world. Expected result: File and project level warnings appear.