Integrate Eclipse debugger with VIM.

This is the first cut of changes to enable remote debugging of Java process
from VIM.

Functionalities
----------------
* Launch/resume a debug session using :JavaDebug command
* Add breakpoint using :JavaBreakpoint command

Usage examples
---------------
1. Open a vim session with servername = default
vim --servername default

2. Open a file to debug in this VIM session.

3. Set breakpoints
Jump to the desired line
:JavaBreakpoint

4. Launch debugger
:JavaDebug start localhost:5000
Assumption: The process to debug is started on localhost and is
listening on port 5000.

5. When the breakpoint is hit, VIM will jump to that location and
highlight it. To resume execution,
:JavaDebug resume localhost:5000

TODO
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* Define a preview window for showing debug variables, etc.
* Show variables, etc.
* Stop debug session.
* Create the document page