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.