When using the btn-group-yesno class on radio buttons in XML forms, the green btn-outline-success is applied to options with a value other than 0.
This causes multiple buttons to be green.

This PR fixes that and more:

1. Changes class of options other than 0 or 1 to be use btn-outline-secundary
2. Fixes issue with the disabled attribute not being added to the options when using the btn-group-yesno class.
3. Fixes issue with the class not being overridable via the xml

Example:

<field name="testing" type="radio" default="0"
	   class="btn-group btn-group-yesno"
	   label="Testing">
	<option value="0">JNO</option>
	<option value="1">JYES</option>
	<option value="2">JDEFAULT</option>
</field>

Before:

After:

Example:

<field name="testing" type="radio" default="0"
	   class="btn-group btn-group-yesno"
	   label="Testing">
	<option value="0">JNO</option>
	<option value="1">JYES</option>
	<option value="2" class="btn btn-outline-info">JDEFAULT</option>
</field>

Before:

After: