Add Vim keybinding unit test [Issue 1762]

Add Vim keybinding unit tests via ace/lib/ace/keyboard/vim_test.js.  Test cases are based on the expected Vim behavior as documented in the online Vim help documentation [here](http://vimdoc.sourceforge.net/htmldoc/usr_toc.html).  Only successful tests are initially enabled.  Additional test cases will be enabled/added as the corresponding functionality is implemented in the Vim keybindings for ACE.