Links to documentation are now using the front-end language to point to the translated documentation page
(except for some links generated from the backend, in the diagnostic tool for example).
Partial fix for #224.
* the front-end now use global constants, based on the translation key
* build-client.js use the ESBuild "define" directive to replace these
globals at compile time, by the english value
* build:client must now be called after build:languages
* moving the loadLoc and loc backend functions in a separate lib
* Builtin Prosody, Share chat url: option to have a transparent background (for streaming integration).
* Builtin Prosody, Share chat url: fixed new day hidding when no scrollbar in readonly mode.
Modal for video owner (and instance's moderators) that allows to generate a link to the chat. So you can - for example - obtain the url to use for OBS integration.
WIP
