Prevent shutdown ordering crashes

Made QGCCorePlugin derive from QGCToolBox and expose everything through the same mechanism as everything else.

_finalize methods need information which is not available if all you
have is a mavlink_message_t

Move battery.percentRemainingAnnounce to Qml Global

The static Fact was causes problems with Qml

offline mission planning settings

more conversion stuff

some fixes and added area unit drop down

Conflicts:
	src/MissionEditor/MissionItemStatus.qml

removed comment

finish unit conversion

correcting typos

Download Speed Tweaks (+2 squashed commits)
Squashed commits:
[ff0ef7e] Cleanup (remove OpenStreetMap)
[370fa1d] Done (+25 squashed commits)
Squashed commits:
[9f3368f] Need to check how many instances of MapEngine are active.
[d557eac] Download Optimization
[392f50a] Almost there.
Trying to optimize download.
[a49d1d2] Settings
[a94be97] Mostly there. Needs to finish options and map thumbnail.
[38d5a0b] Downloading tiles and deleting sets
[81101b9] More UI Work
[c597d4b] Downloading tiles
[a815e35] Get rid of OpenMaps
[7e177ea] More reorg
[fa6b671] Start handling create tile set
Fix signal order when creating fetch tile task
[2a31f4d] Refactoring
[268b906] Renaming things
[947d66e] Fix resource load error.
[19e2de8] Adding MapBox
[c73e627] Preparing download
[87bbf22] UI Tweaks
[3c32a86] A lot of UI code done.
[ece8ce2] Starting to deal with tiles
[7f387bc] Save tile set
[f66f343] Adding more code
[4de3418] Working
[f0cc25d] Done for the night.
[2d1d86e] Added SQL database for holding out own tile cache.
[d405a87] Convert to camel case as this has been driving me nuts.

- New mission command editor dialog
- New MissionCommands toolbox object to get command info
- Added APM mission item set

Windows OS doesn’t disconnect port when you pull plug on USB. This
caused all sorts of problems with previous logic. New logic handles
this correctly.

Also reflow settings pane to take less space

- Pervasive change to automatically connect to known board types
- Lots of additional changes along with this:
- More exposure of objects/properties to Qml
- Much restructuring in LinkManager and LinkManager clients

- Pervasive change to automatically connect to known board types
- Lots of additional changes along with this:
- More exposure of objects/properties to Qml
- Much restructuring in LinkManager and LinkManager clients