Implemented groupable defvars. Variable.Variable: * Added the member `__group` with corresponding getter `LocaleString group()` and setter `this_program set_group(LocaleString name)`. * Also changed all `void` to return the object being called to enable chained calls. defvar("myvar", Variable.Variable(...)) ->set_invisibility_callback(cb) ->set_group("My Group"); Config tags: * emit#module-variables checks if any groups are defined in the variable list, and if so group those together. If an item is a group the mapping will contain the members `is-group`, `group (the name of the group)` and `vars (the list of variables in the group)`. CFIF/template: * The tag definition `<cfg-variables>` handles the emission of grouped defvars.