Accept any URL scheme in markdown links, not just http(s)

[JornWildt]

A markdown link such as [TEXT](http://example.org) works as expected, however, if you want to use a custom URL scheme for a local app, then it fails.

Try for instance [TEXT](myapp://path-to-item) and you will get:

<a class="..." href="" node="[object Object]" target="_blank">TEXT</a>

This is related to the markdown in the content of text elements.