enable 'cd://' for every file access

[Diaphteiros]

How to categorize this issue?

/area usability
/kind enhancement
/priority 5

What would you like to be added:
There are currently several places where files from the blueprint filesystem can be 'imported', e.g. for deployitem templates. Wherever it is possible to access a file from the blueprint filesystem, it should also be possible to access a file resource from the component descriptor instead. Both cases could be distinguished by adding a scheme prefix to the path, like cd:// for component descriptors and blueprint:// for blueprints, with the latter one being the default if no prefix is specified.