Updated copyright date
Updated help/.gitignore
Removed deprecated symbols
Replaced gtk_*_store_append/set with gtk_*_store_insert_with_values
Added properties can_default and has_default to add_button in gnac_file_chooser
Replaced gtk_list_store_append/set with gtk_list_store_insert_with_values
Used libgnac_gstu_bin_add instead of gst_bin_add
Code cleanup