Add a standard set of colours to sitemaps

This adds a standard set of colors to sitemaps, and translates these colors within the openhab UI to the CSS format. Any other color/name/definition that someone may want to use as a color will be passed straight through without modification.

The text below is proposed for the wiki...



openHAB supports a standard set of colors, based on the CSS definitions. This is a set of 17 colors that should be supported by any UI. The colors are defined by name, and within openHAB they are translated to the CSS color format (ie "#xxxxxx"). This should ensure a standard interface for these colors.

Below is a list of the standard colors and their respective CSS definitions. Note that case is not important.

| Name used in sitemap | Color provided in REST interface |
|----------------------|----------------------------------|
| MAROON  | #800000
| RED     | #ff0000
| ORANGE  | #ffa500
| YELLOW  | #ffff00
| OLIVE   | #808000
| PURPLE  | #800080
| FUCHSIA | #ff00ff
| WHITE   | #ffffff
| LIME    | #00ff00
| GREEN   | #008000
| NAVY    | #000080
| BLUE    | #0000ff
| AQUA    | #00ffff
| TEAL    | #008080
| BLACK   | #000000
| SILVER  | #c0c0c0
| GRAY    | #808080

For any color other than those defined above, _"color"_ is passed directly through to the UI, so its exact implementation is up to the UI. It is generally expected that valid HTML colors can be used (eg "green", "red", "#334455") but a UI could for example define abstract colors that are defined internally depending on the theme. For example, "warning" could be defined and used in a UI dependant way, but there is currently no standardisation of these terms.