Add FindBugs Maven integration to the build

This pull adds the findbugs maven plugin into build. 

- The build right now is set to not fail. 
- Only security and performance related bugs are scanned by the plugin.

I'd like to address the findings in separate pulls and once we have everything in order, we could then change the configuration to fail on error. 
This merits a bit of explanation:

Confidence of 2 means, normal level of confidence in the detection of bugs. (1 being the highest, 3 being the lowest)
Ranks 1-14 are considered somewhat serious. 15 and above are like "Fine, but nothing serious for the moment".