Set switchbuf to use tabs while switching buffer.
Suspend/resume specific thread.

* Go to thread window and run :JavaDebugThreadSuspend or
  :JavaDebugThreadResume to suspend or resume thread under cursor.
  If there is no thread found under cursor, then the entire debug
  session is suspended or resumed.

* UI improvements and bug fixes to thread window. Support running debug
  commands from the status window by defining them in those windows.

* Got rid off plugin/debug.vim as the commands are now defined inside
  the status window itself.
Code refactor.

* Created separate packages for context and event.
* Created separate event handlers instead of cramming everything inside
  DebugEventSetListener. It simply delegates to appropriate event
  handlers - ThreadEventHandler and DebugTargetEventHandler.