This adds a new feature to `Flash` that allows to pin it after a
specified selector. This removes a fixed position from such award-emoji
alert, and makes it responsive by design of selector that this alert is
pinned to.

Closes #3996

Make sure we wait for AJAX request to finish before end test and cleanup
database

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

[ci skip]

This makes it more intuitive, as user can see that something actually
happened after adding emoji-only comment in long discussions.

This reverts commit 63144cd0, reversing
changes made to 8ab5df9d.

Use RJS to render edit note feature.

Before:

```
Rendered projects/notes/_note.html.haml (27.9ms)
Rendered projects/_zen.html.haml (0.3ms)
Rendered projects/notes/_hints.html.haml (0.7ms)
Rendered projects/_md_preview.html.haml (3.9ms)
Rendered projects/notes/_edit_form.html.haml (6.9ms)
Rendered projects/notes/_note.html.haml (17.7ms)
Rendered projects/_zen.html.haml (0.3ms)
Rendered projects/notes/_hints.html.haml (0.6ms)
Rendered projects/_md_preview.html.haml (3.4ms)
Rendered projects/notes/_edit_form.html.haml (7.0ms)
```

After:

```
Rendered projects/notes/_note.html.haml (13.8ms)
Rendered projects/notes/_note.html.haml (7.1ms)
Rendered projects/notes/_note.html.haml (9.5ms)
Rendered projects/notes/_note.html.haml (8.5ms)
```

This change reduce at least 6ms * N ('N' - number of notes).

This fixes the file upload dialog which currently works for new comments
but not for comment editing. The cause for this is a missing DOM class
which causes traversal to the dropzone to fail.

This is fixed by adding the expected `gfm-form` class to the edit form.
It has to be added dynamically since adding it to the form template
would break the form's layout and comment saving.

Closes https://github.com/gitlabhq/gitlabhq/issues/9283

Addresses #2221.