fix(config): make it possible to init app with empty domain

you can use `app.register_resource` to define your domain but
if you start app with empty you get an exception.
fix(datalayer): make datalayer usable outside request context

fix when using datalayer outside request context but within app one
Merge branch 'fix-datalayer-app-context' of github.com:superdesk/eve into superdesk-fix-datalayer-app-context
Data layer usable outside of request context.
Merge branch 'superdesk-fix-datalayer-app-context' into develop
Fix ?version=all/diffs bug preventing full response
Merge pull request #377 from joshvillbrandt/version_all_diff_bug

Fix ?version=all/diffs bug preventing full response
Merge branch 'develop' of github.com:superdesk/eve into superdesk-develop
Start app without any defined resource.
Merge branch 'superdesk-develop' into develop