Removed CSS rules which don't appear to be used anywhere.

This is a precursor to also testing (and implementing) that a chat pages
through MAM results (see #1549)

Remove unused method.

Also add a new API method `api.disco.features.get` for the use-case
where you still want the feature object to be returned.

- Use native `getTime` method instead of moment's `valueOf`
- Use toISOString() instead of moment().format()
  This makes the code timezone independent since we're now globally using UTC.

Messages (received directly or via MAM) are stored in a backbone
collection that's kept sorted by the message's "time" attribute.
Various parts of the codebase rely on this behavior.

For regular messages, the time attribute is generated by
`moment().format()`, which generates a timestamp in the browser's
local timezone, for example "...+02:00".

For MAM messages, we would previously copy the "delay.stamp" value
into the "time" attribute verbatim. However, that value is generated
by the server and is unlikely to be in the same timezone locale.

ISO timestamps expressed in different timezones cannot be sorted
lexicographically, breaking the premise of keeping the messages
collection sorted by time.

instead of accepting a callback functions.

Room auto-configuration broke if the config form contained fields with type `fixed`

Legitimate carbons messages blocked due to erroneous forgery check

* Rooms Api
number of parameters in the documentation was made 2 from 3 as api which is used to open a room with default configuration has only 2 parameters.

it is debounced and otherwise we might enter a state where reconnection
no longer happens.

- Add a new method to check for dupes based on the message text.
- When checking for dupes based on origin_id, no need to restrict to
  only our own.

Since those commands aren't only about moderation

Ideally Snabbdom wouldn't completely replace the input when we add the
`error` class, because that's what's causing the input value to be
cleared.

That way we don't lose the user's input values, we avoid flashing and we
avoid unnecessary rendering.

In the process, fixed an annoying issue where Chrome auto-completes
what it thinks is the username into the "Language Tag" field of the MUC
config form.

Instead we tell Chrome that the MUC JID is the username, thereby also
letting it save the password to to that JID.