Eagle Tree Pilot Tube Sensor: Fix calibration and airspeed computation.

The sensor was being miscalibrated because the division was wrong. This
fixes the issue, as well as cleans up the defines.

It also changes the airspeed calculation to occur only when the pressure
is positive.
Add style sheet for inverted horizontal sliders.
Refactored input and output channel reversing. This involved
simplifying the code, as well as removing checkboxes and
replacing with less ambiguous visual clues.
Remove unused reverse button.
Changed behavior so that the spin boxes would wait for the user to finish
before updating the neutral slider.
Added swap icon.
Added reverse icon button.
Output config: Automatically set the maximum spinbox values for output PWM pusle width.
BoardManager: Add virtual keyword to getChannelBanks()
OutputChannelForm: Change to qint32.
Output config: Resolved race condition

Previously, a race condition would occur when the ActuatorSettings UAVO
was updated before the board was recognized. This led to the spinbox
settings not being updated correctly.
Changes requested in review.
Merge pull request #760 from kubark42/reverse-channels-button

Reverse channels button
Merge pull request #980 from kubark42/output-pwm-maximum-as-function-of-channel-frequency

Output pwm maximum as function of channel frequency
Merge pull request #1002 from kubark42/fix-eagle-tree-calibration

Eagle Tree Pilot Tube Sensor: Fix calibration and airspeed computation.
Merge remote-tracking branch 'remotes/origin/next' into next