Insert Git commit hash into build artifacts

[Godin]

For better source traceability we should insert the Git commit hash into the build artifacts:

• As a MANIFEST.MF header in all JARs
• Into index.html (linked with Github)

A shortened hash can then be used for the JaCoCo runtime identifier.

[Godin]

Relates to #7

[Godin]

@marchof Could you please verify my changes? Generated JAR files now should contain Eclipse-SourceReference entry with proper "commitId" (issue #7), but index.html wasn't modified as I'm not sure what you wanted to change in it.

[marchof]

Header looks good to me -- but does not work for Eclipse. If I try to import a plug-in built with the new header from the repository I get the error message "The plug-ins do not have an Eclipse-SourceReferences manifest header that can be processed". I'll investigate.

[Godin]

Hm, FYI I took an example from https://bugs.eclipse.org/bugs/show_bug.cgi?id=380691

[marchof]

Ok, I give up. I wasn't able to import any project with a git URL, not even a org.eclipse project. So this seems not to be our problem. -> We can merge this.

[Godin]

@marchof Seems that this feature is a part of EGit 2.0 and requires Eclipse 4.2 - see http://wiki.eclipse.org/EGit/New_and_Noteworthy/2.0#Support_for_Eclipse-SourceReferences_manifest_headers

[marchof]

I tried EGit 2.2 but on Eclipse 3.8.1.

[Godin]

@marchof I was able to successfully test this feature from this branch with a fresh installation of Eclipse 4.2.1.

[Godin]

Done in 4a77e40