merge the build processes of socorro and its new django webapp

the build systems didn't come together as smoothly as anticipated. submodules need to be updated before django runs through its build process. django can no longer update them itself since it is no longer in the top level of the git repo, so it must rely on the general socorro-repo bootstrap.

this also involves a refactoring of the makefile to accomodate the changes, add documentation, make the targets more explicit, and eliminate redundant or unnecessary targets