feat: component based popovers

Until this MR, popovers were very limited. To add new kind of items meant to update VUI itself and play with a single big component. The item definitions were in a plain object. This is not an optimal solution. I rewrote the entire popover component so that it uses subcomponents.

This approach requires user to write more complex templates than a single json object but it gives them power over all the subcomponents and events that are firing. User can handle mouseover/mouseenter events or add their own components to the base item component slot...

The implemented child components are:

• FwPopoverItem - A base for all child components, also a button
• FwPopoverSubmenu - Basically a submenu that has opening/closing handled automatically
• FwPopoverCheckbox - A Checkbox button with boolean v-model
• FwPopoverRadio - A FwPopoverCheckbox dynamic list with a string v-model and choices property that is a string array

The largest (last) example from docs is recreated at the bottom of the docs. I haven't updated any other examples. Hence I'm assigning @Sporiff. If you want to update the docs, I'd be pleased.

Note to a person working on docs: Just look at the example or ask me what is used how. There are 2 things that are internal and shouldn't be documented (or should be marked as an internal API in the spoiler or something). They're prefixed with undocumented.