Simplify status fields.

- Previously had three status fields wizard_status, status, and
sf_status.
- Reduced to just wizard_status and status.
- Added necessary scopes to easily find Student Applications and
Projects by status.
- Salesforce sync now operates with “status” field both ways.
Remove placeholder course sites info.
Correctly mark Student Applications as "complete".

Previously only “wizard status” was being updated. Now student
applications will properly be set to “complete” once all wizard steps
have been fulfilled.
Refactor dashboards.

Simplify project and student dashboards.
Use partials for field host and student dashboard.
Apply correct permissions settings to reserve_my_spot
Further fixes to enumerize/status fields.
Change styles for form errors to prevent layout issues.

Overlap error on input field to avoid extra span breaking column
layouts.
Initial version of seat filling logic.

Only allow students to apply to projects that have seats available.
Only approved student applications count towards seat limit.
Seat limit is enforced on a project session level.