VIM-439: Implement :sort command.

- Supports "n", "i" and "!" arguments.
VIM-660 Handle <C-Space> as pressed keystroke, not typed one
VIM-665 Handle Shift-char as typed uppercase keystroke, not as pressed one
Removed obsolete Vim help action for <F1>
VIM-651 Parse <BS> as backspace
VIM-648 Use default keymap if there is no previous keymap in config

Keymap upgrade message has been improved.
Removed unused method
VIM-661 Apply Normal mode mappings only at command start
Vim shortcuts handler is enabled for keys associated with IDE if there are no shortcut conflicts
Merge remote-tracking branch 'selesse/vim-439'

Conflicts:
	src/com/maddyhome/idea/vim/ex/CommandParser.java
New IdeaVim API compatibility
Added |:sort| to index
Added Alex Selesse to the list of contributors
Fixed nullity warnings
Immutable local variables where possible
Local class name conventions
Nullity and immutability
Updated CHANGES
Updated CHANGES
Use original Up/Down actions for non file-based editors