Add description to projects

[s-espinosa]

Background

• Emma has had to collect project descriptions over Slack. It would be easier if this was just required when projects were submitted.
• We have not been using the notes column since demo night is no longer a part of graduation.

PR Description

• Add description to projects table.
• Add description to new project form for a default user.
• Remove note from new project form for a default user.
• Add description to admin user form to edit a project.
• Add validation for description to Project model.
• Update error message that displays to more clearly indicate that a description is required.
• Update project creation spec.
• Add feature spec to confirm description validation.
• Add model spec to confirm description validation.
• Update spec project factory to include description.

[s-espinosa]

@notmarkmiranda Merged based on the approval, but interested to hear what you think about the explanation for the merge in the ProjectsController.