Add flag to disable local signups
- Defaults to enabled
- Custom signup link is still shown if configured
[#73324702] https://www.pivotaltracker.com/story/show/73324702
Remove accidentally-committed cache disable for Thymeleaf templates.

[#73324702] https://www.pivotaltracker.com/story/show/73324702
Remove create account routes when login.signupsEnabled is false.

[#73324702] https://www.pivotaltracker.com/story/show/73324702