[LanguageSelection.py] add summary description for selected Language

Example for skinners for the two Language-screens:

	<screen name="LanguageSelection_summary" position="0,0" size="256,64">
		<widget source="parent.summarylangsel" render="Label" position="0,42" size="256,22" zPosition="1" font="FdLcD;20" halign="center" valign="center" />
	</screen>

	<screen name="LanguageWizardSummary" position="0,0" size="256,64">
		<widget source="parent.summarylangsel" render="Label" position="0,42" size="256,22" zPosition="1" font="FdLcD;20" halign="center" valign="center" />
	</screen>

Example for the AudioSelection-screen:

	<screen name="AudioSelection_summary" position="0,0" size="256,64">
		<widget source="parent.summary_description" render="Label" position="0,42" size="256,22" zPosition="1" font="FdLcD;20" halign="center" valign="center" />
	</screen>