From the island of misfit fixes

Various fixes that have little in common.

Main tweak was to allow table th tags to be used, I choose the most complicated path to impress emanuele :dancers:  Something had to be done since the editor with a cut paste will send th tags to parsebbc / preparse so we either ignore them, convert them to td or deal with them as headers.  I chose the last but there could be some glitches in that should someone just want to send in junk layout.