String fields in modedata_t structures are filled in via functions that
return 'gchar *' pointers - adjust structure data types and release
function accordingly.

The modelist_free() function uses g_list_foreach() iterator and a
callback function that is not appropriate for the action, and then uses
a cast to hide any compiler warnings - get rid of the cast by using
g_list_free_full() iterator and a suitable callback function.

The modelist_load() function looks complex and indiscriminately loads
all files from dynamic mode configuration directory. If there are for
example editor backup files present, this can lead to hard to detect
issues - simplify the logic and use glob pattern expansion to derive
list of files to load.
Signed-off-by: Simo Piiroinen <simo.piiroinen@jollamobile.com>