Recorder: Add snapshots manager

Added snapshots manager - a dialog to select and delete snapshots which are created when recorder plugin is active.

Added button "Remove snapshots" to the third step of the Export timelapse dialog.

Screenshots:

Test Plan

"Clean up Snapshots" dialog:

• A new "Manage snapshot directories" button must appear in top right corner of Recorder docker
• on click a "Clean up Snapshots" dialog must appear.
• Clicking Select All/Deselect all button must select and deselect all the items.
• When selection is changed the "space to be freed" label must show the actual info.
• When "Clean up" button is clicked only selected directories must be removed.
• The indeterminate progress must be shown when (re)reading snapshot directories and deleting snapshots directories.

"Export timelapse" dialog:

• The third step of "Export timelapse" should have a new "Remove snapshots" button.
• When clicking it, only snapshots directory for the current document must be removed.

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.