Useful for testing parts of the code, but only distribute it.

Simple helper function that makes it easier to get the
location of the desktop file. The uri is also valid
in almost all GFile locations, so therefore no filename
function.

Most likely garcon will only be used in normal applications,
so calling g_type_init() is handled by gtk_init(), if not
the user should call it.

For now an application implementing garcon should call
garcon_set_environment (...) before using any of the functions.
This will leak the string once, so if you want to avoid this
call garcon_set_environment (NULL) when the app exits..

Implement this in a new function garcon_menu_directory_new,
just like we do in GarconMenuItem.

Because the object is implemented as a singleton we can
use a global lock in the file. The advantage is that
we can drop our g_thread_init() call in garcon_init(), so
the user can initialize garcon from every place in the
code.

Make the funtion easier to read and test for regular files
in the user's directory too.

Also drop the {set,get}_filename API since it's not really
safe for remote files. Setting the filename had no function
anyways.

We're going to use something based on GFileMonitor, so drop
the old code since it also conflics with the API changes
that will be committed to GarconMenuItem.

Use a GFile for garcon_menu_new() and a filename for
garcon_menu_new_for_path(). This matches the API change
in the pervious commit.

We use GIO for file loading internally. The two convenient
functions allow creating a GarconMenuItem from a filename or uri.

This reverts commit 3e471653.