Add Colorize tool

[xeolabs]

Related to #100

• Extend xeokit-sdk BCFViewpointsPlugin to save and load the colorized state of each object.
• Add a "Colorize" tool to the BIMViewer. This would work like the Selection tool, but would just colorize the objects. This would mean that they don't appear ghosted and floating. The Colorize tool would also allow the user to configure the current Colorize color.

[Amoki]

Colors are already handled by BCFViewpointsPlugin :)
https://github.com/xeokit/xeokit-sdk/blob/master/src/plugins/BCFViewpointsPlugin/BCFViewpointsPlugin.js#L592

[lanjoni]

How can I colorize a object and save? Without a external metadata...