[TimerEntry, PowerTimerEntry] add summary-description for Timerlog-scree...

...ns

Example for skinners for the screen:

	<screen name="TimerLog_summary" position="0,0" size="256,64">
		<widget source="parent.Title" render="Label" position="120,0" size="136,40" font="FdLcD;17" halign="center" valgin="bottom" />
		<widget source="parent.summary_description" render="Label" position="0,42" size="256,22" zPosition="1" font="FdLcD;20" halign="center" valign="center" />
	</screen>