Determines whether search suggestions are shown in the "Add Contact" modal.

We need it for mobile where (eventually) we might have the participants
sidebar occupy the whole screen.

such as <https://example.org>

We need to wait for the state to be fetched from storage before
rendering the list.

* Ensure that outgoing messages are also marked as single emojis
* Also set msgid to origin-id for sent groupchat messages

When set, the "Nickname" field won't be shown in the "Add groupchat"
modal and instead the nickname will be automatically set (based on other
config settings).

above other nickname sources.

This is a fix for https://github.com/conversejs/converse.js/issues/1508

when creating attributes for outgoing message.

Otherwise `id` is the same for all messages.

Until now, we've only been explicitly documenting the `_converse.api`
namespace and only considered the methods under it as forming the API
contract (which determines how we do semver releases).

It appears as if we've reached a point where trying to keep everything
under the `_converse.api` namespace no longer makes sense. Certain
methods are applicable to particular models and trying to shoehorn them
into the `_converse.api` namespace seems clunky and non-intuitive.

I've therefore decided to slightly refactor `sendMessage` to let it take
two simple parameters and to document it with JSDoc so that it's
presented as an API method, albeit only available on a chat model.

updates #1496
updates #1504