Generate application scheme manually

Letting Xcodeproj create the schemes for us didn't work super well. It created
a scheme for each target individually, and there was no way to set the test
target. We also had to manually move the scheme from the user's data directory
to the shared directory.

Note that at this moment, Xcodeproj sets the testable bundle name to 
name.ocunit instead of xctest. Xcode corrects this when it opens the project,
leading to a dirty repo.