New features
- "Hide terrains with furnitures" option in the palette explorer.
- Tile defined "fill_ter" is shown when selecting the option "Only show
defined in prefab".
- The fields of the palette explorer are editable and should allow for
easier copy/pasting. Note: the modifications are only visual i.e. the
acctual palettes are not modified.
- The "coordinate seletor" tool displays an input box with the
coordinates (in addition of setting the clipboard).
- The "coordinate selector" supports areas (in addition to points) using
mouse press and drag.

Bug Fixes
- Duplicates of palette entries when loading (and reloading) prefab.
- Missing "rows" field appears with a proper warning text (instead of
"null pointer exception") in the error log.