Add bracketcolors plugin. Color {}, [], () based on nesting order

Closes geany#1148

* simple UI

* start hooking up signals

* mechanism to save settings from a conf file

* save load settings for defaults button

* less globals

* better config color name

* hook up colors

* glib types

* use colors from plugin config

* update colors when settings change

* reorganze, try to avoid giant files

* update document colors when they switch

* update headers

* fix bug when some brackets werent getting added to bracket map

* fix bug that was deleting newly inserted brackets

* std::map insert doesnt overwrite, use insert_or_assign

* handle when removing a bracket completes another

* handle invalid color specs in config file

* avoid static initialization fiasco

* if there are problems loading config, use defaults

* cleanup headers

* mark GUI labels as translatable

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Co-authored-by: Asif Amin <amin@arlut.utexas.edu>