Implement color for phrase/para

[tomschr]

This PR fixes #453

Use <?dbsuse color="..."?> inside <phrase> or <para> or use the attribute role="color:...". Currently, the following colors are supported:

• SUSE brand colors suse-jungle-green, suse-pine-green, suse-midnight-blue, suse-waterhole-blue, suse-mint, suse-persimmon, suse-fog
• "Typical" CSS color names aqua, black, blue, darkgray/darkgrey, fuchsia, gray/grey, green, lime, maroon, navy, olive, orange, purple, red, teal, white, yellow
• RGB colors with the syntax #RRGGBB (wheres R, G, and B are a single hex digits)

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TODO after discussion with Jana (2022-05-31):

• [x] Disallow CSS color names and RGB colors
• [x] Define also shade SUSE colors

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Examples and screenshot

```xml ✓ Hello Hello ```