Fix rendering of custom emoticons
The regex for detecting custom emoticons is not good enough to detect some of the variants in the wild. Since any attempt to create a regex that is powerful enough is futile[0], this instead makes neochat not show previews for and linkify any mxc urls, which it detects by the /_matrix/media/r0/download/ path of the url. This does mean that we don't have previews and linkification for other cases of mcx urls though; IMO this is acceptable since having these urls in normal messages is rare anyway
[0] https://stackoverflow.com/questions/1732348/regex-match-open-tags-except-xhtml-self-contained-tags
Edited by Tobias Fella