fixed mixers/FMU_MuMROV.mix - motor 4 lower limit was at +4000, had to be -4000
- fix mixers/FMU_MuMROV.mix
- tune controller gains
Merge branch 'temp_backup'

Conflicts resolved:
	ROMFS/px4fmu_common/mixers/FMU_MuMROV.mix
Merge pull request #8 from axelh/master

mixer bugfix and controller tuning