Implemented CallHierarchy for Java (caller/callee)

Closes #134.

Included eclim command, vim scripts, vim documentation and some attempt
at testing. Ran checkstyle.

I was unable to run the tests as no matter what target I used for ant,
it constantly tried to overwrite files in my eclipse folder. Will try
to look at it again with more attention tomorrow. In any case, I tested
manually around the eclim source code and it appears to be working.

I based the code on C's CallHierarchy. I left the maximum depth at 3
since that's what appeared on the C example but I think it would make
more sense to set it at 2 because with big projects it takes quite some
time (up to 5 seconds on the execute method of the implemented 
command in eclipse). We could then employ a system on the vimscript 
to ask for more call hierarchy on a particular element like what is done in 
the GUI. I'm not very experienced with VimScript but it seems doable 
(code similar to NerdTree, etc) and would bring it closer to the Eclipse 
GUI behaviour and performance.