Remove needless try/except
Refactor upgrade steps

- Move the upgrades module to its own folder to make it easier to maintain
- Refactor tests to avoid issues with next profile version
Add behavior to enable reloading the current page after a certain amount of time
Avoid NotFound: ttl error under Plone 4.2
Return default value in template if TTL field has not been initialized

This seems to happen in Plone 4.2 (Dexterity 1.2.2).
Merge pull request #457 from collective/refresh-behavior

Add behavior to enable reloading the current page after a certain amount of time
Merge branch 'master' into issue_420