treewide: rework uci change display

treewide: rework uci change display

 - Use native rpcd uci changes format instead of incompletely converting
   back and forth between the old and the new format
 - Rework uci changelog template to print the equivalent uci commands
   for the various changes
 - Rework theme headers to properly count the uncomitted changes
 - Rework theme CSS to properly style new changelog

Fixes: #2170
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit 849d153851db2fc193c1c82648dbe719463d3a38)