TabConfig UI settings and styling support

[fabriciomurta]

Found: 7.2.0 Ext.NET forums' thread: Ext 5.x with Spotless Theme Variants

Ext.NET 7 currently has no support for tab panels' UI settings as Ext.NET 5 used to. Additionally, the custom UI CSS for the themes that support in v5 is not included at least with the Gray theme for v7.

An example to try to use this is, based in Tab Panels > Basic > Show/Hide example, add this CustomConfig block to one or more panels:

<customConfig>
    <ext-add key="tabConfig">
        <ext-add key="ui" value="danger" />
    </ext-add>
</customConfig>

Ext.NET 5 lacks styling for the Aria, Graphite and Material themes (#1439).