Multiple Playtime instances should never share the same items

[Benjamin Klum]

Currently this is possible for example by:

1. Duplicating the Playtime track
2. Saving the current Playtime setup as a preset and loading it in another Playtime instance (essentially the same as 1)
3. Filling a slot of Playtime instance 2 with an item that is already used in Playtime instance 1

This introduces weird behavior such as disappearing clips and strange playback behavior (makes sense).

[Benjamin Klum]

re #80 Ask user whether to copy item on "Fill slot with item" if it's already in use

→ <<cset 85bde11b7c8b>>

[Benjamin Klum]

re #78, re #80 Provide slot context menu action "Fill with copy of selected item"

→ <<cset c791773f9579>>

[Benjamin Klum]

re #80 Ask user if Playtime should duplicate already-in-use items on preset/project load

→ <<cset 0c008ea88968>>

[Benjamin Klum]

re #80 Don't complain if item is already in use by slot that is currently filled

→ <<cset 80fd99e01ce4>>

[Benjamin Klum]

re #80 Correctly reposition items vertically if duplication on load

→ <<cset f6d70e957a4f>>

[Benjamin Klum]

Resolved in upcoming 1.2.1

[Benjamin Klum]

re #80 Better wording in duplication dialogs

→ <<cset d0460914740d>>

[Benjamin Klum]

re #80 Fix non-working duplication on preset/project load on OS X

→ <<cset 68ff921d0df7>>