Fix displaying current and target temperature for non-Pro models on Prepare Temp screen

[phillipthelen]

The Screens used for PAGE_PREPARE_TEMP and PAGE_PRINTING_FILAMENT by the Pro includes a label for current and target temperature each (probably because of the changed layout bc of the segmented bed). The equivalent pages for the non-Pro display both values in the same field separated by a /. Currently the display connector can not join two values into one field, so the label currently only displays the current temperature and the target temp is only shown in the text field above. I almost have the changes finished to join multiple values into one label, which would enable this to be done.