Improved comments and disabled debug prints (editor)
Added persistent list-like shelf (database)
Use dicts for metadata in editor (instead just lists) for better readability and preparing it for persistence
Fix several issues with persistent list (db):

 * Support slices
 * Remove no longer used references (in the base dict)
 * Preserve updated items (rows)
 * Minor improvements in readability
Improved metadata handling, fix cut/paste, avoid initial modification events
Integrate metadata support with the database
Fix total time calculation when null & possible division by 0
Fix NULL condition in database query
Add ordered iteration in database list shelf
Track modification phase in new metadata (directly in the editor)
Add dict like keys method to database list shelf
Removed old metadata (pickled) support

There is no need to calculate any diff now, as the editor updates the phase directly in the metadata
update metadata text on change
Allow rollback on database shelves
Support several database connections per session
Isolate metadata db connection per each file
Store or revert metadata on editor save/close

This sync the metadata with the file text when user saves the changes or abort them
Fix metadata initialization (first line)
Unify and minor refactor to GetLineText

 * Strip newlines for metadata
 * Use the same method than the debugger