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

fixes #1352

updates #1352

updates #1352

Eventually we need to add better support for receipts and markers of MAM
messages.

We'll need to do the following:

* First check whether the MAM page already contains the receipts or markers, to avoid duplication
* Only ever in catchup mode
* Only after full catchup to ensure that the receipt is not in a different page than the message

Currently, in order for Converse.js to recognize a pasted URL as an
image, it must be an URL whose protocol is `https:` (`https` in the
URI.js library's notation). This is sensible, but means that any
non-HTTPS image URL is not recognized as a valid URL (and thus will not
be rendered inline, even if `show_images_inline` is set to `true`).

It is important to always check for HTTPS URLs when in a secure context
(i.e., the initial page load was requested via HTTPS) in order to ensure
that non-secured content does not mix with secured content. However, the
inverse is not true: if the original page was loaded over HTTP, then
enforcing HTTPS for images adds arguably no meaningful protection while
also breaking the `show_images_inline` feature for the edge cases where
Converse.js is deployed without HTTPS and a user pastes an HTTP URL.

This patch changes the behavior of the `isImageURL` method such that the
requirement for the pasted URL's protocol to be `https:` is enforced
only when the `window.location.protocol` itself is also `https:`. By
doing this, we ensure that secure origins (i.e., when Converse.js is
loaded over HTTPS initially) are still secured and cannot have non-HTTPS
content introduced to the page via a pasted non-HTTPS URL, however it
also allows non-HTTPS origins to render both HTTP and HTTPS image URLs.

Before the function `extractReference` in
`/src/headless/converse-muc.js` matched url and email.

Fix: https://github.com/conversejs/converse.js/issues/1327

With MAM2 we can just use stanza-id

This helps us to avoid duplicates by relying on the fact that Backbone
models have unique ids.

Update Lithuanian (lt) translation

As per XEP-0004, the default "type" of data form fields is
"text-single", so a missing "type" attribute should not be treated
differently.

This fixes handling of CAPTCHAs offered by ejabberd.

Removes the need for maintaining a map of keycodes to keys