Sampler feature

Selecting the grid size and then hitting "apply", now hides unnecessary
samplers
Sampler fix

Pushed the playhead position to the beginning of the file whenever a
sample is loaded into the buffer
Sampler fix

buffer~ won't work with a numbers only argument name
the buffer name must contain alphanumeric characters
Sampler fix

the message "/play 0" sets the playhead to the beginning of the audio
file
Sampler fully implemented

The sampler feature is now working, but still needs proper testing!
(should the sampler have a "change" object after the "/play" message
???)