Use new getMatchLabel() to get the text to match elements against.

With the changes for preference pages, previous getLabel() and
getSortLabel() had a target conflict regarding matching vs sorting vs
display. The cleanest way to match against not displayed text seems to
be to make the match string explicit instead of reusing these methods.

Change-Id: I15ea22475d25e8007bcd1ae5663cbc6431cb508d
Signed-off-by: Carsten Reckord <reckord@yatta.de>