modal: make block (closes #798)

- [x] main idea
- [x] bh templates + tmpl-specs
- [x] specs
- [x] gemini tests
We don't have `_visibility` modifier. If you about `_visible_progress`, then how should it work? 
AFAIK we can't set new value to modifier in his `onSetMod`-handler. 

Usage of `animationend` looks good, but we will be forced to use two css-classes for animation: first for setting/unsetting `display:block` and second to setting/unsetting `animation-name`.