Clearify naming of url and uri

[thmarx]

In some places we mix url and uri. For example the PathUtil.toURI creates the url for a contentFile, to be used for navigation in the frontend.

We should make that more clear any maybe refactor some of the places.

Keep in mind, that maybe some modules has to be modified as well.

[thmarx]

I think we should use the following convention:
uri: its a path of file in the filesystem
url: web url or path to build weburls