Use smooth fade in/out for effect enable/disable

Affects: equalizer, compression. The rest of changes are just
minor API updates.

Equalizer fade in/out is perfect. It is configured to take about
2 seconds.

Compression remains is difficult because android gives us
volumes only after enabling has happened, thus, easily causing a
discontinuity. For this reason, compression always fades in from
full silence. Fade out is seamless, however.

Change-Id: I61b49555185fbc9020445fa69098f3e815e579bc