[facet js] minor refactoring and cleanups
* extract facetCheckBoxSelect and facetCheckBoxUnselect
* use $ as prefix for jQuery variable (facet -> $facet)
* other minor rephrasing
option_group_changed('port', 'main', 'web')
option_group_changed('query-log-file', 'main', 'web')
option_group_changed('profile', 'main', 'web')
option_group_changed('max-post-length', 'main', 'web')