Fix latex render in annotations

We need
  disconnect(textEdit, SIGNAL(cursorPositionChanged()), this,SLOT(slotsaveWindowText()));
and it's counterpart, otherwise when inserting the image, the cursor pos changes, slotsaveWindowText is called, the content is passed by a toPlainText and set again and kaboom the content is lost

Also a few extra const

BUGS: 335476
FIXED-IN: 4.14.2