Handle missing PNG in dw2pdf export

Add button to download diagram PNG if it exists in cache

Attach download and open buttons to diagrams

ensure only diagram files can be edited/selected

make everything work :-D

Prosemirror: don't submit the form on button presses

Handle titles and dimensions in prosemirror

Select files in media manager in Prosemirror

Simple Prosemirror menu button and edit form

refactor the media manager integration

Add ajax backends for loading/saving embedded SVGs

This also renames the syntax classes to be easier to distinguish

first go at refactoring the diagrams editor into a class

Catch insufficient permissions early

If user has no permisssions to create a diagram in current namespace,
remove the form altogether.

Missing letter in en/lang.php

Rename plugin to diagrams

Create diagrams in a modal dialog

Add MIME configuration check

Allow editing only diagram files, respect media ACLs

Extract language strings