small fixes to the .desktop file

Remove deprecated keys encoding (utf-8 is now mandatory) and TerminalOptions Add keywords (keywords should be included, not necessarily exactly these keywords) Icon should be specified by icon name, not by exact path, when installed on a system Added mimetypes as submitted to freedesktop shared-mime-types, will file a MR for mimtypes installable by the package later. Add a way to open files. This is not implemented yet, but I expect it to be by beta release?