Move progress out of project

[blutz]

Make into its own table that is related to a Project (but not a goal). Schema:

ProgressEntry

• id: ID
• project: fk(Project)
• created_at: datetime
• entry_date: datetime
• value: number (decimal, 0.00 precision)

Don't worry about existing data (i.e. it's okay if the migration is destructive).

Sub tasks:

• Create db migration
• Update API to work with current UI. Minor changes are needed to associate progress with project instead of goal. Goals should inherit their progress from their parent project

Next step: #19