Glue on fill not necessary if take just has different start offset

[Benjamin Klum]

If we manage to restore the original take offset when starting to play instead of taking offset 0, glue is not necessary.

[Benjamin Klum]

Multiple improvements and fixes:

• re #187 Memorize original take offset and use that as initial offset for every play operation instead of zero
• fix #186 Fix behavior of continue and gate offset modes with playrates != 1

→ <<cset 88b33f34fdfb>>

[Benjamin Klum]

Fix #187 Restore initial take offset on next project load if project is saved while playing from another offset

→ <<cset 7fb1f9910d34>>

[Benjamin Klum]

With the implementation of #3, the take start offset now serves as anacrusis! So a glue is necessary again if you don't want anacrusis. But it makes sense. Out-of-measue loop borders would probably confuse people.