Fixes #14968

**Bug**
Due to https://github.com/chjj/marked/issues/829, markdown escapes inside of links are currently not rendered properly. This also can effect regular text that contains characters that are escaped when we convert them to markdown text.

**Fix**
For links, remove markdown escapes before rendering them.

* Make markdown image dimensions configurable using a custom image renderer

In the newly introduced syntax extension the width and height of an image
can be given in the image title using following format:
![image](someimageurl 'caption|height=200, width=100').
Both width and height parameters are optional, if they are not given the
width and height attributes remains unset on the image element

This resolves #14803

* Change size parameter location to href part