#7726: show inline images of multipart/related message parts

#7726: show inline images of multipart/related message parts

- replace cid urls in images with getResource query link (by adding new
custom URIScheme)
- removed some obsolete code from TransformURI class
- implemented test
- this is part 2/2 for #7726
- added Felamimail.getResource to FMail HTTP frontend

https://forge.tine20.org/mantisbt/view.php?id=7726

Change-Id: I3c21594b5e88f128ae957f9c389c0407278b87d2
Reviewed-on: https://gerrit.tine20.org/tine20/2210
Tested-by: jenkins user
Reviewed-by: Philipp Schüle <p.schuele@metaways.de>