Less saves in the palette docker

I added a "Save" button to the palette docker and smart autosaving in various cases.

Current behaviour:

• just editing the palette doesn't create a new version of the palette
• clicking Save button does create a new version of the palette
• closing Krita normally does create a new version of the palette if the palette was modified
• switching to another palette does create a new version of the palette if the palette was modified
• crashing Krita loses the unsaved changes to the palette

Concerns:

• now the "Save" button is basically only used in case when Krita crashes - so is it even needed? is the icon good? Maybe I should add a separator between swatches edit buttons and the other buttons? (also what's up with that remove button... wouldn't a trashcan be better?)
• maybe Save shouldn't create a new palette version if the palette was not modified?
• should changes on palettes that are document-embedded be shown? They will be saved anyway. If the user saves, that is.

Notes:

• for exporting the palette, there is a separate export button in the palette chooser

To do:

• ensure it works after Dmitry's fixes to resources versions
• ensure it updates thumbnails on saving a new version
• don't show changes on files that are not global (since they will be saved anyway into the document)

Test Plan

1. Creating a new global palette

• go to the palette chooser, click the + button, put a name for the palette - it should create an empty palette for you. It should be visible after restarting Krita under the same name. It should have the same colors as before.

2. Saving normally

• edit the palette
• use the Save button
• close and open Krita
• changes should be there, there should be no copies of the palettes in the list

3. Switching to another palette

• edit the palette
• switch to another palette
• changes should be there, there should be no copies of the palettes in the list
• the name should look as if it was saved
• close and open Krita, the changes should be there

4. Just closing Krita

• edit the palette
• close Krita
• changes should be there, no duplicate palettes

5. Crashing Krita

• edit the palette
• crash Krita
• no changes saved!

6. Crash + save before

• edit the palette
• use the Save button
• crash and reopen Krita
• changes should be there, there should be no copies of the palettes in the list

7. Crash + switch to another palette before

• edit the palette
• switch to another palette
• changes should be there, there should be no copies of the palettes in the list
• the name should look as if it was saved
• crash and reopen Krita, the changes should be there

8. Create a new document palette

• create the palette inside the document
• save the document
• reopen Krita
• open the document
• the palette should be there

9. New changes in the palette

• open a document with a palette
• make changes
• overwrite the file
• the changes should be there

10. New changes in the palette - new file

• open a document with a palette
• make changes
• save to a new file
• the changes should be in the new file
• old file should still show the old palette

Formalities Checklist

• I confirmed this builds.
• I confirmed Krita ran and the relevant functions work.
• I tested the relevant unit tests and can confirm they are not broken. (If not possible, don't hesitate to ask for help!)
• I made sure my commits build individually and have good descriptions as per KDE guidelines.
• I made sure my code conforms to the standards set in the HACKING file.
• I can confirm the code is licensed and attributed appropriately, and that unattributed code is mine, as per KDE Licensing Policy.