Options/Choices refactor

I have finally completed and merged my refactor of the NetSurf user
option code.

This means that user options files will now only contain the options
which differ from the defaults. This will alow us to alter the
defaults in future and have everyones choices actually update instead
of being overidden by old saved default values that might not be useful.

There may be a small but annoying side effect to this chnage in that
many people will have bad default settings saved in their Choices
files already which will now be faithfully applied even if they are
unwanted.

The principle place this will be observed is with system
colours. These are the colours exposed as specifically named css
properties [1] and can be seen on test pages [2]

NetSurf also uses these colour settings throughout the UI for several
platforms. Each platform sets its own defaults and the users
configuration is available to override these settings.

Up to this point the system colour configuration and setup has been
somewhat flawed and will probably have resulted in most users saved
Choices containing a set of overrides setting all these colours to
black! (0)

If you experience such behaviour with CI builds after #1212 please
edit your Choices file to remove all the entries beginning with
"sys_colour_" they should not reappear subsequently (unless you would
like black controls, labelled in black on a black background, with a
little black light that lights up black to let you know you have done
it.)

[1] http://www.w3.org/TR/css3-color/#css-system
[2] http://www.iangraham.org/books/xhtml1/appd/update-23feb2000.html

--
Regards Vincent
http://www.kyllikki.org/