Create a sub class of QTreeWidget
Drag of WMS nodes
Removal of debug message
Add an extra blank line
Refactor of FavoritesTreeNode

Add a subclass for each type of nodes
Removal of tests on the type of nodes
Removal of an unused import
Drag and drop for any type of layer
Removal of unused mime type
Don't allow drag and drop within the plugin dock
Make the folder node the default one
Update of the metadata files

Fixes #19
Merge branch 'dragndrop' into develop