set servo8 min-max for heli default params
improve heli-dual default params
modified dual heli default params for new sitl model
allow spool up time for heli takeoff
Try to make the various param files to follow similar namings:
- Lowercase the few ones using uppercase
- Use dash to separate name components
- Start with "copter", "plane", "rover", etc instead of the mix we
had
- Remove "params" from the filename since it's redundant with the
extension