Make project URL an explicit field

Create an explicit field in the project edit template for defining the handle (e.g. `http://codeforphilly.org/projects/{handle}`)

Use JS to auto-populated based on title

When editing an existing project, reveal a note that a redirect will be created after the handle is edited. Create the redirect automatically on save

Start in the project edit template and trace the save path for existing projects. Check how the title is exposed to JavaScript and how project URLs are currently generated; done means the handle can be edited, is auto-populated from the title, and saving an edited handle creates the stated redirect.

Written by the indexing model from the issue text.