SVGHMI: rework Jump widget to cope with Enable Expressions.

Relative jumps are not disabled implicitely anymore when pointed HMI_NODE is 0.
Also, "activable()" implementation was enhanced to make it optional.

[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