move screen DPI and refresh rate entries into Screen menu
fix #765
display OTA update menu only on Kindle and Kobo
add OTA settings for server mirrors and channels
reorder setting entries in reader menu
update pot file
negative x panning if writing direction is set right to left
so that in right to left writing/drawing system the right part
of the page is drawn first
Merge pull request #766 from chrox/master

add OTA settings for server mirrors and channels