Added support for automatically adding checklist templates to all new review

checklists for a user.
Added an evolution which adds a field, 'auto_add' to ChecklistTemplate that 

determines whether they should be added to all new checklists made by the user.

In the UI this is represented with a checkbox as shown in the attachment below.
The templates are added when the checklist is created which happens the first 

time a user loads the diff page for a review they haven't seen before.
Additional templates and items can still be added to a checklist that was

initially populated with default template items.
These changes depend on the changes in review request #7960.

Manually ensured that the evolution migration worked without errors on

reviewboard-2.5.x with the previous checklist schema.
Ensured that the auto add fields toggle correctly and get loaded 

correctly on the templates page in My Accounts.
Ensured that new only those templates marked with the auto add flag are 

added to every new review checklist created by the user.
Regression testing to confirm that making templates, adding checklist

items, checking them off, deleting them, and so on still work.