Remove 511-character limit on configuration file lines

Tested-by: Kai-Martin Knaak <knaak@iqo.uni-hannover.de>
Remove 509-character limit on configuration values

Tested-by: Kai-Martin Knaak <knaak@iqo.uni-hannover.de>
Store full library path with menus
Add support for recursive directories to GTK library dialog
Load footprints recursively from subdirectories
If there is only one library root node, keep it expanded