Allow modules to be bypassed

[nickdowell]

Raised by @ZbigniewB in #129

I think it would be handy to have ability to switch-off whole modules of synthesizer just by clicking their namefields (say: by clicking white letters "Reverb" one could switch reverb off completely with no need to change its parameters; the letters could then turn to gray or red to mark "inactive" state). Presently something like this I can see only in "Filter" module (I mean its "Bypass" menu option). Of course initially, after amsynth has been run, everything should be "on" by default.

[VOC-LINK]

Meanwhile I've got another suggestion: to allow select the size of interface. Present interface is barely readable on currently used resolutions; so IMHO it would be convenient to have 3 sizes to choose from:

• present one as "small"
• 2x larger as "medium" (this is what I would need for today, to conveniently operate Amsynth)
• 3x larger as "big"
• ...and in addition maybe even 4x bigger as "huge" (for future resolutions, who knows...)

[nickdowell]

The latest release (1.11.0) added support for scaling on HiDPI setups! This scaling follows the GNOME scaling setting, but could be made user configurable if that’s useful.

User selectable sizes would be a great feature but currently not feasible until the UI is moved away from GTK #37