Annotations.

The use-case here is that you have a Xournal document, you'd
like to put textual comments in it, but you want it to be easy
to strip out those comments when exporting to PDF (say you're working
on a presentation).  So it would be handy to have a different type
of element which has exactly this toggleability.

In principle, we can apply this to all items, but text is what
I really needed.

As a visual cue that it's annotation, I apply a transparency. There
might be better ways to do it.  This transparency is NOT APPLIED on
PDF generation.

Button/cursor image choice is atrocious.

An alternate way to nirvana is to have a different layer mechanism
which is not per page but global.  This seemed a bit of fiddling
about.

File format extension: new 'annot' attribute on text elements.

Copy paste format modified.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
ctrl+shift+D accelerator for Delete Page

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
Release 4.8~ezyang20130803

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>

Release 4.8~ezyang20130912-1.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>

Release 4.8~ezyang20130912-2.

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>

Release 4.8~ezyang20131023

Signed-off-by: Edward Z. Yang <ezyang@mit.edu>

Release 4.8~ezyang20140925

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Release 4.8~ezyang20140927

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Release 4.8~ezyang20141002

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
Disable image resizing based on bounding box

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
Support for "Duplicate Page"

Keyboard binding: ctrl+D

Supports undo/redo

Preserves layer structure!

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
Add accelerator for New Page After (ctrl+shift+n)

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
Adjust current page based on viewport middle.

This algo works pretty poorly when pages are extremely small
relative to viewport size (essentially, it is very difficult
to get a focus on the first/last pages); however, I find it
a lot more user-friendly for figuring out which page I'm on when
dealing with mid-sized pages.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
Release 4.8~ezyang20141015

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>