Use shortest possible string for colours

[Johannes Höhn]

Currently Inkscape is always using #rrggbb when outputting colors, when using standard settings.
There also is an option to always use CSS colour names, when possible. This option also enables #rgb output when possible.

This patch removes the option and always just uses the shortest possible string for the colour.

[jazzynico (jazzynico)]

Why should we remove an option that allows users to choose exactly the behavior they want?
I'm pretty sure that forcing the shortest possible string for the color would cause a new report claiming the change is a regression...

[Johannes Höhn (johannes-karl-hoehn)]

The only usecase I see for editing SVGs produced by Inkscape using a text editor is to reduce the filesize. Something this patch actually does while also reducing code size.

I see several problems with the current code:

 - The user doesn't know why she/he should set/unset the option.
 - The user could confuse this with the SVG 1.2 tiny feature of defining own named colors
 - The standard setting is the one with undesirable effects for most of the users of Inkscape, as it produces larger files.
 - It's not communicated that only this option also generates the shorter #rgb type color strings.

This also doesn't have much to do with the user's choice. If the users wants to format the SVG into a certain format she/he should use a formatter. There are lots of color formatting options that aren't supported (the rgb(x,y,z) format for instance)