Add name and external_id fields to project_url

[fyliu]

Overview

We need to add name and external_id fields to the project_url table, which was decided here.

Action Items

• [ ] Add name and external_id field to project_url
  • [ ] ERD
  • [ ] Spreadsheet
  • [ ] Code
• [ ] check and release #78 from ice box

Resources/Instructions

• add name field: What the link is called Ex: Primary Repo, Secondary Repo, Description of "other" type urls
• add external_id field: resource id provided by github or google
• both fields should be varchar(255) or CharField(max_length=255)
• external_id can be blank