Add bar numbering alignment options

[DomClark]

Adds options to change the bar numbering system in the piano roll and automation editor. The options are:

• Relative to clip: bar numbers start from 1 at the beginning of the clip. This is the current behaviour.
• Relative to clip, aligned with song: bar numbers start from 1 at the first point of the clip that corresponds to a bar line in the song editor.
• Relative to song: bar numbers match those in the song editor.

I thought there was an issue for this, but I can't seem to find it. Feel free to link it if you find it.

Most of the changes are in order to get quantisation to work with a grid that doesn't start at zero. As a side effect, loop point snapping matches editor quantisation for the piano roll and automation editor now, not just the song editor.

Fixes https://github.com/LMMS/lmms/issues/3907

[Veratil]

#2375