New rc calibration channel widget

Left QGCRadioChannelDisplay alone so that I didn’t need to modify all
the other APM board code which uses this control. Also new control only
support horizontal orientation, with no plans to add vertical.
Added new RCChannelWidget
Update to new QGCRadioChannelDisplay API
RCCalibration updates

- Updated to use RCChannelWidget
- Removed attitude control widgets
- Previous calibration values now shown when not actively calibrating
Merge pull request #836 from DonLakeFlyer/RCWidget

RC Calibration Updates