Raised idle RPM and enable low-pass-filter

Idle RPM was to low for my combination of Turnigy Park 300 motors and the
BLHeli ESCs, so I raised it to 1250, same as on my NanoQuad. Due to the
vibrations of the motors (low quality), I enabled the low-pass filter to
remove some of the jitter.
Merge branch 'nanowii-35cm-wheelbase' of github.com:hmbusch/MultiWii into nanowii-35cm-wheelbase