Rename classes

[alranel]

Goals:

1. Align class names to the final Modulino names
2. Avoid collisions with other libraries by prepending the Modulino word as a namespace

Current name	New name
Buttons	ModulinoButtons
Tone	ModulinoBuzzer
LEDs	ModulinoPixels
Encoder	ModulinoKnob
Distance	ModulinoDistance
imu	ModulinoMovement
barometer	ModulinoAir

As discussed, we will only provide classes but no singletons/externs. Users will declare their instances explicitely in the sketch.