gio-tool: Various fixes related to error messages

This patch contains the following changes:
- Print all errors with "gio: " prefix
- Print file uri in error for each tool allowing multiple locations
- Mark all error messages translatable
- Do not leak strings used in error messages
- Always start error messages with capital letter
- Unify some error messages across various tools
- Fix addional/missing new line characters

https://bugzilla.gnome.org/show_bug.cgi?id=776169

gio/gio-tool-remove.c

@@ -67,7 +67,7 @@ handle_remove (int argc, char *argv[], gboolean do_help)
 
   if (argc == 1)
     {
-      show_help (context, _("No files to delete"));
+      show_help (context, _("No locations given"));
       return 1;
     }