Add API checking using clirr

Add API checking using clirr

In order to generate API reports run: mvn clirr:clirr

The reports are generated to the folder
target/site/clirr-report.html under the respective
project.

In order to check API compatibility and fail the build
on incompatible changes run: mvn clirr:check

For now we compare the API against the latest release
1.1.0.201109151100-r.

Bug: 336849
Change-Id: I21baaf3a6883c5b4db263f712705cc7b8ab6d888
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
Signed-off-by: Kevin Sawicki <kevin@github.com>