Now we have
-----------------

- base
- form
- danger
- prev, next
- icon, image
- iconButton, imageButton

Where:

- base, form, danger define color
- the rest define functionality

6.3 Goal
-----------------------

Separate css (color) and type (functionality) so that we can have any "typed" buttons with different colors:

~~~
type:"iconButton", css:"webix_primary"
type:"image", css:"webix_danger webix_primary"
~~~

Css:

- webix_base (default, alias to webixtype_base)
- webix_danger (alias to webixtype_danger)
- webix_success (green button)
- webix_warning (yellow button)
- webix_primary (makes any prev variation raised)

Backward compatibility:

- type:"form" is "webix_base webix_primary"
- type:"danger" is "webix_danger webix_primary"

Next, prev

- Not relevant, we may omit giving extra css for them (styling arrows is sad)