Improve setModified behaviour and journal checkpoints

[Jan125]

setModified behaviour is currently inconsistent. Tempo, Global Transpose, and Global Volume for example get added to the journal, but do not call setModified. Muting, Unmuting and Soloing tracks set neither, but are saved in the song, so they should set both.

The first commit moved the setModified check to the journal. On project load with instrument plugins, several blank? journal entries are created, that to my knowledge don't do anything.

The second commit removed AutomatableModel.cpp line 307: addJournalCheckPoint(); This fixes the blank? journal entries on load. I am currently checking if there are any unintended changes. So far, I have noticed none.

This draft will get updated as I work through this.