VIM-265 Add window split commands

Conflicts:
	src/com/maddyhome/idea/vim/VimPlugin.java
	src/com/maddyhome/idea/vim/ex/CommandParser.java
Removed unused declarations
Cleanup
VIM-770 Close the current tab on :quit instead of all tabs with the current file
Added salaam to the list of contributors
Merge branch 'vim-265'

Conflicts:
	AUTHORS.md