Add attribute "is_locked" to project model

[mjstealey]

Add attribute is_locked to project model

• [x] include boolean is_locked in project model - default to False
• [x] add logic to "lock" project while membership is being modified - ensure to unlock if anything fails along the way
• [x] allow only read calls while a project is locked (all PUT or PATCH calls should be dropped with a 423: locked response)
• [x] include string expires_on in project model - set to project creation date + PROJECTS_RENEWAL_PERIOD_IN_DAYS (365 days)
• [x] prevent project from being edited if it is_locked or has exceeded the expires_on date
• [x] add method to alter expires_on date as facility operator (as datetime string)