Supporting multiple projects on magma

[graft]

We would like to be able to have multiple 'projects' contained within Magma. Each project might have its own data hierarchy, models, validations, etc. The separation is only to (1) avoid mixing the concerns of different projects (2) allow some nuance in data representation (one project's gene expression data might differ from another's in some important way) and (3) provide some basis for authentication.