Replace invalid solr control chars with space

Also don't clean the text when it's saved with as a Page

The invalid control chars include newlines, so the text looks
pretty bad with all the newlines removed.

This saves the text as-is, then cleans it when it's sent to solr
Allow newlines, carriage return, and tabs
Clean text as it's inserted
Remove leading '0' from form feed regex

\0 isn't super helpful in stripping chars