Sub-projects Management: Dashboard or pop-up form

Much like users will need an interface to manage Volunteer Projects which are children of CiviEvents (see VOL-104), users will need to manage a Project's sub-projects.

Ideally, these two very similar interfaces would share a lot of code. That may mean we build the form in PHP and deliver it as a pop-up, rather than write it in JavaScript. The technical approach remains to be determined.