CI: Use Project Settings Warning

[wurstbroteater]

Travis produces the following warning:
[WARNING] Parameter 'useProjectSettings' is set to true, but preferences file '/home/travis/build/tthuem/VariantSync/de.tubs.variantsync.core/.settings/org.eclipse.jdt.core.prefs' could not be found!

In this pull request #53 we decided to remove the .settings folder, but as it can be seen, it is possible to tell Travis, Maven, Tycho to use the project settings (like org.eclipse.jdt.core.compiler.source=1.8) which are defined in org.eclipse.jdt.core.prefs.

Todo:

• Discuss if we should add the .settings folder and the org.eclipse.jdt.core.prefs file again.
• Investigate how the CI behavior changes if we use the Project Settings or not

Hint:

• It is possible to define for example the compiler version in the org.eclipse.jdt.core.prefs file. Is it possible to use other compiler?
• Maybe this tackles the problem of "strange workarounds so the project might work in eclipse AND intellij"
• Details https://stackoverflow.com/questions/15927484/is-settings-org-eclipse-jdt-core-prefs-part-of-the-project