Refactor task locking

[cdausmus]

Task locking is currently done by checking the task views. A clean up and refactor is required to achieve the following:

• Easier locking logic for admin task view, task locking
• Specific lock timeouts for project type
• Consistency across task locking and admin view

Changes:

• Add a new lock column to task table (with user of who locked the task)
• Lock: view task; Unlock: save/skip task, timeout specified by project type
• Project type admin: specify lock timeout - DO NOT allow modification of project type name.

Requirements:

• As current; Transcribing a task locks for all users
• Display lock for self, 'Locked by you!'
• On task load, check if locked (in case of stale Admin page), especially validate. Display error page stating lock details and links to return to admin page (if validating).