Add "theme" option to Enums like ButtonColor

[FoobarLegend]

We're using an Admin template that uses css selectors like "btn btn-outline-theme", note the -theme suffix. We don't want to create a new Component that extends the BlazorBootstrap button but ideally have the option to use the "theme" option for selecting from color related Enums.

For example:

<Button Color="ButtonColor.Theme" Type="ButtonType.Submit">
   I am a button
</Button>

that would translate into:

<button type="submit" class="btn btn-theme">I am a button</button>