Clean up workflow and tasks when project is archived

[FyreByrd]

Currently, when archiving/reactivating a project, all it does is set/unset Project.DateArchived.

Suggested behavior for discussion:
On Archival:

• Clean up all user tasks for the project
• Do something with the workflow instances.

On Reactivation:

• Recreate all user tasks for the project
• Reverse whatever was done to the workflow instances on archival.

While archived:

• Prevent modification of project except for reactivation.

[FyreByrd]

The current behavior matches S1. We will want to change this later probably

[chrisvire]

This seems to be an important enough enhancement that we are going to include it in S2. Let's keep this simple.

On Archival:

• remove user tasks

On Reactivation:

• reassign user tasks

It seems like we can use the same code when a project is assigned to another person. If the project is in the archived state, then no one is assigned to it.

At the moment, I don't think we need to worry about preventing modification.