OP-1198 allow GCS gadgets to store/restore individual state (needed for OP-1194)
OP-1194 scope gadget will now persistent plot and legend visibility state between runs

+review OPReview
OP-1194 minor cleanups to scope gadget state persistence handling
OP-1233 added make options to skip qmake and build single gcs dir
- add QMAKE_SKIP=1 on make command line to skip qmake
- add MAKE_DIR=<dir relative to ./ground/openpilotgcs> to compile that directoy only
- example : make gcs QMAKE_SKIP=1 MAKE_DIR=src/plugins/coreplugin
- use at your own risks ;)

+review OPReview
Merge remote-tracking branch 'origin/next' into filnet/OP-1194_persist_scope_gadget_plot_and_legend_visibility_state
OP-1194 uncrustified
Merge branch 'filnet/OP-1194_persist_scope_gadget_plot_and_legend_visibility_state' into next
Merge branch 'filnet/OP-1233_add_make_options_to_skip_qmake_and_build_single_gcs_dir' into next