Apply pull request #1502 provided by bstroebl: Add ntv2 entry for Thuringia
do not transform toString to quote values (NULL integer becomes 0 otherwise)
[FEATURE][composer] Implement an item tree panel for composer windows
(fix #4358). Allows for selection of items, hiding/showing items,
toggling lock status of items and double-clicking to edit item id.
Don't double add features
Fix #10969
[composer] Remove right-click to lock for composer items (fix #5592), now that locked items can be unlocked from the items panel this is no longer required, and frees up right clicks for a composer context menu
[composer] Locked items can't be selected by clicking them in the canvas.
[composer] Deselect items when they are locked from the items panel
[composer] Decrease default snap tolerance to 5 pixels
fix editing of NULL values (fixes 0 to NULL, and fixes setting of NULL values in postgres)