Includes filetype, non-FT and execute groups.

Fixes https://github.com/geany/geany/issues/3385. Fixes #705. 

## Further work This does not set menu accelerators, that can be done later. Also it would be good to move the fixed commands into the relevant groups - like compile, build into the filetype commands group - again this should be done separately. You can view, comment on, or merge this pull request online at:

https://github.com/geany/geany/pull/3394

-- Commit Summary --

* Add keybinding groups for custom build commands * Move custom commands below build group * Fix kb strings leak * Refactor with setup_group_size * Update docs

-- File Changes --

M doc/geany.txt (13) M src/keybindings.c (113) M src/keybindings.h (8) M src/keybindingsprivate.h (10)

-- Patch Links --

https://github.com/geany/geany/pull/3394.patch https://github.com/geany/geany/pull/3394.diff