Added ESC calibration procedure.

The button for ESC calibration was added to Output page next
to "Test outputs" checkbox. It walks user through the whole
process of calibration, beggining with channel selection that
allow to select specific outputs.

This feature was requested and can be closed here:
https://github.com/TauLabs/TauLabs/issues/1177

Reported-by: cGiesen Signed-off-by: Ivan Sevcik ivan-sevcik@hotmail.com