[Control]: Change multirotor autonomous modes to use
AttitudePlus.
Added GUI support for multirotor attitude+ mode.
Moved trim buttons to global widget. Correcting level bias with
attitude+ will always work for every vehicle frame.
1) Slightly refactor so that combobox slot does not depend on
specific combobox string.
2) Turn on servo level trim conditionally.
Renamed slots so that QT doesn't make an automatic signal
connection.
Add tooltips for trimming buttons.
[GCS]: Add dialog box to inform user of the success of the trimming operation.
Merge pull request #949 from kubark42/mr-attitude-plus

Add AttitudePlus support to Multi-rotor airframes.