Enhancement: Ability to disable sync to clock

[riban-bw]

The documentation says that ALO will synchronise to a clock if it is present else works as a standalone looper. It would be advantageous to be able to manually chose whether to use clock, standalone or automatic.

I use ALO on Zynthian which has a master clock that runs whenever a step sequence is running. ALO detects this and synchronises very nicely but one might want better of different control over the mode of ALO.