IDE: fix completion

uses ctrl key on Mac
update internal variable list before listing them
avoid exception if empty list
apply selection when pressing return or enter

[main]
host = https://www.transifex.com

[beremiz-ide.beremiz]
file_filter = Beremiz_<lang>.po
minimum_perc = 0
source_file = messages.pot
source_lang = en
type = PO