First stab at adding basic text only annotations

First stab at adding basic text only annotations

Shift-other button within a page should open up $EDITOR command where
one can enter the text associated with an annotation that will be
placed under the cursor, in this case, upon normal exit,
save-path-command (can be as simple as `echo /tmp/modified.pdf')
result will be used to save the file with the new annotations to.