Make the command line editable

The user can now edit the command line (when inputting commands or making a search).
  * This can be done by either:
     -  clicking the command line;
     -  pressing ARROW LEFT (goes to the end);
     -  pressing HOME (goes to the beginning).
  * The edition can be terminated by:
     - pressing ESC,
     - deleting everything (BACKSPACE)
     - executed by pressing RETURN
  * Since the command line is just a regular textbox, clipboard access becomes a handy bonus ;)

Signed-off-by: Antonio Inacio <ja.te.disse@hotmail.com>
Minor cleanups
Merge branch 'editcmdline' of https://github.com/w1ndig0/VsVim into testmerge
Formatting changes

Convert tabs to spaces
Restructured the VimBufferTest suite
No longer beeps on first Left arrow

The command line editting was beeping the first time the <Left> arrow
was hit.  The <Left> key was making it's way down to the Vim layer which
didn't understand how to handle <Left> in command mode and hence beeped.

The fix was to have the CommandMarginControllor intercept the <Left>
event and handle the key itself.
Minor cleanup