Investigate testing with GWT Mockito

[spg]

The current test suite uses Selenium tests. Though they cover a lot of potential issues, they are complex to write and maintain.

We might investigate https://github.com/google/gwtmockito to see if some units of code could be refactored and tested using standard JRE tests.

[jDramaix]

I think gwtmockito is not very compatible with GwtQuery ?