pdf: saving quadrilaterals

Adding back-end support for saving quadrilaterals
of annotations.
Implementing get_text_layout_for_area

Added the method to the interface of document-text
and an implementation to ev-poppler. This will be
used for drawing text markup annotations.
view: preparing for interactive annotations

Added a struct to the view that holds start and
end points of annotations in order to support
'click and drag' annotations. Changed the creation
point from button_release to button_press.
Defining annotation icon size
Add get_bound_rectangle for text markup annotations

Implemented a function that returns the smallest rectangle covering all
quadrilaterals of a text markup annotation.
view: function for reloading a rectangle

The responsabilities of creating an annotation and
reloading the corresponding region of the view are
separated.
view: adding text markup annotations

Implemented the creation of text markup
annotations in view.
view: saving annotation area in mapping

Once the button is released, the annotation area
is saved in the annotation mapping.
Only text annotations have popups

Removing the popups from appearing automatically
on text markup annotations.
Annotation default colors

Highlight: yellow
Strikeout and underline: black
Squiggly: red
Adding sidebar icons to add annotations

Adding icons to add highlight, strike out,
squiggly and underline. Line and free text still
depend on updates of poppler.

Based on kcm's (Anuj Khare) patch.