Add fallback for Color.fromCssColorString

[nf-s]

Add fallback for Color.fromCssColorString

The type signature for Color.fromCssColorString(col:string) => Color is incorrect as it can return undefined.

For example, this catalog has a CSV with an enum color map with an invalid CSS color:

• http://ci.terria.io/next/#clean&https://gist.githubusercontent.com/nf-s/e89bc5da84fb5f41d205d02287841abe/raw/2dfad06e6421b7942fd3f3da4b1d62a1cbf50f2b/colorstringtest.json

When the catalog item is added to the workbench the map will crash.

This PR adds default colors for wherever Color.fromCssColorString is used.

I also deleted some old JS files:

• lib/Models/LegendHelper.js
• lib/Models/TableColumnStyle.js
• lib/Models/TableDataSource.js
• test/Models/LegendHelperSpec.js
• test/Models/TableDataSourceSpec.js

Checklist

• There are unit tests to verify my changes are correct or unit tests aren't applicable (if so, write quick reason why unit tests don't exist)
• I've updated CHANGES.md with what I changed.

[KeyboardSounds]

Can you fix the type declaration in terriajs-cesium as well? We're using custom type decs for Cesium still I think so it's a problem on our end. Unless we're not, in which case we should create an issue in Cesium, because sharing is caring.