Fix opening files over http

[Khaled Hosny]

We used to support this, but it has been broken since the switch to using glib for parsing command line because the lines:

file = g_file_new_for_commandline_arg (remaining_args[i]);
path = g_file_get_path (file);

in startui.c do not return a bath in case of non-local URI.

One way to address this is to port our IO to glib’s gio so we can work on GFiles directly, which will give us many of GFile goodies for free.

[Khaled Hosny]

Re-enable opening fonts over http

Fixes #25

→ <<cset 68565fc1ced3>>