#240: Improve locking configurability

Currently it is too easy to lock a content item without realizing that one has done so.  This happens when entering edit mode (either full edit mode or inline edit mode) and then failing to hit the Save or Cancel button.  Since locks never timeout in the default configuration, this results in littering the site with locked items which may be confusing to users.

Additionally, it is not possible to disable locking or change the lock timeout value without monkey patching plone.locking, as far as I can tell.

 This proposal is intended as a quick fix to the existing locking implementation, rather than a more far-reaching refactoring as is discussed in http://plone.org/products/plone/roadmap/189

I propose that, at the least:

• The default lock timeout for locks created through the web should be 5 minutes.  A periodic KSS action can extend the lock as long as the user remains on the page.  Locks created through other means such as WebDAV should still default to never timing out.

Additionally, we should consider:

• Create a configlet to turn locking on/off and adjust the timeout value.
  

 Initial implementation completed and submitted for Framework Team review and merge to Plone 3.3 release.

David Glick is willing to serve in an advisory role to whoever is willing to implement this.