Hide Trash item in Places if trash:/// path isn't accessible.

It is better not show Trash item if it cannot be entered.
Adopt bookmarks handling from gtk-2.24.12

Since version 2.24.12 gtk+ honors gtk-3 style of bookmark file placement
so default GtkFileChooser may behave different from LibFM.
This commit adopts those changes and LibFM is compatible with GTK again.
Remove obsolete comment from autogen.sh about --enable-gtk-doc is required
Deprecate get_folder() VTable method in FmFolderView

The folder is retrieved from model in any case so this one isn't required.
Let make future simpler.
fm_finalize() should save the same file name which was loaded.

It saves always libfm/libfm.conf now.
Commit adds data info FmConfig where the name is stored and fm_finalize uses it.
The former behavior for NULL (i.e. default) stays the same.