Styles & history & copy-pasting: refactor

[aurelienpierre]

That code is unmaintainable, slow, does many redundant operations, and most of it is not thread-safe.

• don't write history immediately back when reading it 0eb29af
• cleanup redundant undo/redo commits to stack d1ae32b
• move xmp writing to a separate thread to prevent filesystem & network I∕O from blocking UI 2d717f8cd5e6ef901c61ab1429048d40176e1f0b
• auto-save history in background while in darkroom
• remove GUI code from dt_dev_history_[add/read/pop]_ext()
• refactor dt_dev_history_[add/read/pop]_ext() to something understandable
• clean up high-level history copy and paste, add debug strings
• clean up high-level styles, add debug strings
• refactor the 3 different methods that write XMP
• add copy-pasting option to mandatorily create new modules in target pipeline/history
• add an app-level DB lock on image's history read/write from library
• don't save histories that didn't change since opening 05ac029
• update DB history hash when writing histories 8ad5c78

[sahlirc]

I guess this observation is related to this issue so I prefer not mention a new bug. In version 1455, one can clear the development history while in the lighttable only, not in the darkroom. This is still improved compared to previous recent versions.

[sahlirc]

I would like to add something new to me regarding "orientation" in the history (I surmise it is part of your WIP, but prefer to mention it just in case). While it is a mandatory module appearing in position 6 on opening my cr3 file consistent with its position in the pipeline, another one is created in position 13, which is not in the pipeline. This one seems redundant as one can fuse it with the mandatory version on compressing the history.

[sahlirc]

Another comment I would like to make is that version 1588 appears as a landmark in the good direction (I do not know where to put this comment, as I am not a great chatter...) with its new tools regarding embedded jpeg, focus zone and selection of row numbers in the top lighttable panel, as well as its overall GUI which is very well thought. I'll get back to you later (as of version 0.0.1?) with suggestions that may be premature to list under this development foundation of Ansel.