Add integration with Rainbow Parenthesis

This commit adds integration with both the classic DrChip Rainbow
Parenthesis plugin and the later Rainbow Parenthesis Improved plugin.
These are used in preference to our own brace folding scheme if these
plugins are installed and enabled
Fix integration with Rainbow Improved plugin

This commit fixes the use of the Rainbow Improved Plugin to configure it
appropriately for SPARQL so that it doesn't interfere with our other
syntax highlighting rules.

There is a bug in the Rainbow Improved Plugin which can interfere with
this for which a pull request has been opened
https://github.com/oblitum/rainbow/pull/13