minor cleanup / reordering of initialiser in Nativeui, also moved finding of localisation files to its own method

Moved sizing controls for battery display, tab_modeswitch, localisation button to ui_layout. Also added more explicite passthrough of intra-widget spacing parameter based on screen size so that it scales more easily

# Conflicts:
#   .gitlab-ci.yml

Updated data handler to tag plot data using cycle payloads, and limit the back data on circle plots to 3 cycles

Redefined base handler class to inheret from QObject since all current handlers use signal functionality

renamed 'handler' to 'payload_handler' to distinguish from the generic handler class (e.g. for text etc.)

handler.set_db now returns 1 for an unrecognised payload type. NativeUI.get_updates uses this to determine if the payload has been recognised, and raises an error if not.

NativeUI can now be agnostic to which handlers do what, it can simply pass all payloads to all handlers.

Merge branch 'merge_layout_abstraction' of https://ohwr.org/project/hev into merge_layout_abstraction