coding style updates for new java debug code
fix message key in DebugStartCommand
rename java debug breakpoint toggle command

- rename the command to toggle breakpoints to make it easier for users
  to scan wildmenu completion for the command.
- rename the java class as well, grouping breakpoint commands together
  (again, easier to scan the list and locate the file)
fix java debug vertical temp windows

not perfect since there are resizing issues as other windows are opened
and closed, but this makes it functional as a start.
Improvements to debug status window.

* Define a command :JavaDebugGoToFile to go to a file when breakpoint is
  hit instead of using --remote-tab. We want to do some more actions such
  as create a sign to highlight the line. Changes are done to VimClient,
  signs.vim, debug.vim.

* util.vim: Function to go to a buffer window even if its in a different
  tab. Function to delete a buffer and its window. Used to auto remove
  the debug status window when debugging session is stopped.