[import] Allow for more advanced imports

[quintesse]

We should add the following features:

• Allow for code located in sub folders, not just the root
• Allow for multiple code-bases to be present
• Allow import of boosters (having one or more .openshiftio/application.yaml file(s) somewhere)
• Allow import of previously created applications (having a deployment.json file in the root)

One suggestion is to have the /import/analyze endpoint return an entire deployment descriptor which can be passed on the the /import/launch endpoint to do the actual work.

This means that the analysis doesn't simply return a single builder image name (which isn't enough if you want to deal with all of the above points) but a complex structure which the frontend can either edit or pass on unchanged.