Renamed "Identity" -> "Annotations" config panel

It only contained an option to set annotations' author name
Make PageViewAnnotator reparse tool list on configuration change

This doesn't do anything useful at the moment. In next patch I'll turn
the tool list into a configurable option.
Turn the annotation tools list in a configurable option

Instead of using a system-wide tools.xml file containing a list of
<tool>...</tool> elements, store each tool element as string in a
stringlist configuration option.
Note that the global tools.xml file is still needed to read the
default values.
Annotation settings: Added stub widget to edit raw XML tool data
Initial implementation of widget to edit annotation tools

It only supports removal, moveup and movedown.
Added support to create new annotation tools
Fixed localization issues

Translate strings when retrieving the default annotation tool list, so
that we can assume that strings in the AnnotationTools setting are
translated.

Note: In future patches, I'll remove i18n strings from the default tool
list at all
Don't hardcode pixmap name in annotation tools' XML description

First step towards dynamically-generated tool icons
Paint some annotation tool icons dynamically

So that they are the same color as the annotations they create.
This patch also adds some new icons.

Affected annotation tools:
 - Ellipse
 - Polygon
 - Rectangle (NEW)
 - Squiggly (NEW)
 - Line
 - Strikeout (NEW)
 - Underline

I'll edit the remaining icons in next patches.
Paint some other annotation tool icons dynamically

Affected tools:
 - Note
 - Inline Note
 - Ink
 - Highlighter

Note that the Stamp tool is the only one that's left with a static icon
Removed unused PNG icons

Note: I'm only removing PNG files; source SVGs are still there
Annotation properties dialog: Moved color and opacity fields from the dialog to the config widget itself

This patch moves the Color and Opacity fields into the AnnotationWidget
class. This will allow future reuse of the same widget to configure
annotation tools.
Note that AnnotationWidget is no longer abstract: a base
AnnotationWidget object only contains the Color and Opacity fields.
Text annotation properties: show the font config field only if the text is in-place
Show the same widget as the annotation properties dialog when creating annotation tools

Note: Some properties are not stored in the tools' XML yet
Added widget to edit InkAnnotation properties (line width only)
Made line width configurable in Ink, Line, Polygon, Square and Circle annotation tools

Note that previously the width attrubute was ignored by the PolyLine
engine and it always set width=1, that's why I had to change the default
value in tools.xml.
Load hoverIcon through our icon loader, because DesktopEntry can't find SVG stamps

With the old code, a "?" icon was shortly shown instead
Removed calls to query size of pixmap size in PickPointEngine::event

Since the size of pixmap is determined by the value of size variable,
we can directly read that variable instead of querying the pixmap.
Also note that "pixmap" comes from "hoverIcon", not from "icon", and
that piece of code wants to know the size of the latter. In case of
stamp annotations, however, they happen to be the same.
Made icon for Note annotations configurable

Unlike Stamp annotations, hoverIcon and icon are different in Note
annotations.
Show tool icons in the configuration widget