Replaces the old suggestion of setting JS head 'window.uploadLimit'
variable. This new env option will be used by back-end validation and
front-end libs/logic too.
Limits already likely exist within prod environments at a PHP and
webserver level but this allows an app-level limit and centralises the
option on the BookStack side into the .env
Closes#3033
- Created new dropzone component.
- Added standard component event system using custom DOM events.
- Added tabs component.
- Added ajax-delete-row component.