dropdown: get rid of wrapping root div node (close #1392)

[aristov]

Resolves #1392

[tadatuta]

why not to generate id automatically by default?

[aristov]

@tadatuta I generate id automatically in template, but if I don't set id manually in tmpl-specs, then I get difference in data-bem attribute, because templaters generate a new id each time.

[tadatuta]

👍

[aristov]

@tadatuta maybe we can consider this case in html-differ and ignore difference for id param in data-bem attribute.

[tadatuta]

@aristov not sure if it's possible as we need to check that id is the same for two corresponding DOM nodes.

[narqo]

1. use elem instead of custom modes in BEMHTML as it was before
2. add tests for proper destruct of popup

[narqo]

applyCtx([
  {
    elem : 'switcher',
    js : this.extend(apply('js'), this.ctx.js),
    ···
  },
  { elem : 'popup' }
])

[aristov]

TODO: ensure that dropdowns mixes work

[aristov]

TODO: ensure that popup's and dropdown__switcher's mixes work

[aristov]

For me: add return before apply*, squash and merge.