Added block cursor colour customisation

This will be useful to those, who uses Vintage mode with Sublime’s
[BlockCursorEverywhere
plugin](https://github.com/jlangston/BlockCursorEverywhere). I’ve used
colour which formerly was used as selection colour (light blue —
#B4D5FE), it plays well with current yellowish line highlight and
selection colours, because yellow and blue are  opposites.
Merge pull request #1 from geraldus/BlockCursorEverywhere-cursor-color

Added block cursor colour customisation