Enable a visibility check for the code completion

With this changes eclim's code completion proposes only elements
that are visible according to Java visibility rules, e.g. private methods
are not proposed.

Unfortunately, I wasn't yet able to get the `CodeCompeletCommandTest`
working. On my system the `completionMissingImportStatic` test case 
fails in both the master and in my branch. Is this okay, or is my setup 
somehow wrong?