JCBC-613: Add checkstyle.

Motivation
----------
We need proper checkstyle rules that need to be enforced across the project.

Modifications
-------------
This change adds the styles we agreed on for now, separate commits will follow
with the actual code changes.

Result
------
Consistent styles!

Change-Id: I79af9e989d65ef17ab7788d6ebffbd7b23e0a054
Reviewed-on: http://review.couchbase.org/43130
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Reviewed-by: Simon Baslé <simon@couchbase.com>