Code refactor.

* Moved the logic of creating debug status window into a separate
  function. This will be used later to pre create the status window with
  empty content and then incrementally updated it.
New command to expand variable value.

* DebugVariableExpandCommand: Command used to expand a variable value
  and show its children.

* Misc: Removed unwanted cache from ThreadView. The results are computed
  on the fly.

* This does not include the VIM side changes.
Define VIM command to expand variable value.

* JavaDebugVariableExpand is a new VIM command. This is valid only in the
  variable window. It will retrieve the child variables and add it to
  the window. This can be triggered by placing cursor on the variable
  line and pressing <Enter>.

* DebugVariableExpandCommand.java: The variables at a particular level
  are returned. No more recursive calls. This should improve the
  performance also.

* Restriced some existing commands to specific window.

* Fixed indentation/fold issues in the debug status window.

* Removed IsCurrentFileInProject check for commands that don't need it.

* Minor code cleanup.
Externalize a few debug UI settings.

* g:EclimJavaDebugLineHighlight: Highlight group to use for showing the
  current line being debugged.

* g:EclimJavaDebugStatusWinOrientation: Sets the orientation for the
  splits inside the debug status windows; if they should be tiled
  vertically or horizontally.

* g:EclimJavaDebugStatusWinWidth: Sets the window width for the splits
  inside the debug status window. This is only applicable when the
  orientation is horizontal.

* g:EclimJavaDebugStatusWinHeight: Sets the window height for the splits
  inside the debug status window. This is only applicable when the
  orientation is vertical.
Fixed folding issues with variable window.

* Hack: Added an empty line to variables that can be expanded. Could not
  figure out a way to get the folding to work without this.

* Another hack: Leaf nodes are indicated with a DOT. Without this, the
  folding does not work as the indentation is different between
  siblings.
Doc update.
Bug fix to open buffer in code window instead of debug window.

If the cursor is in debug status window while stepping through code, we
need to move to the code window before opening the target buffer.
Otherwise, it would open in the debug status window.
code style fixes
update JavaDebugStart arg validateion

set command nargs to * so we can inform the user of example usage if
they don't supply any args, instead of vim's generic message.