Add option to provide a custom lifetime for the access token, using an input field

After working with this module, and figuring out a workflow for page approvals on a project im working on. I got a request that it would be nice to have an option to create a custom lifetime for the access token, on both the configuration page and on the node edit form.

My thought is that when the module is enabled, you still have all of the current lifetime options in the dropdown, with an additional "custom" selection. When that is selected, a text input field shows up below the dropdown that allows the user to input in a custom hour value. Or it could be more specific to allow the user to input the day, hour, and second fields. Then when you save, the module calculates the duration of the custom values, and saves that duration value in seconds like the rest of the lifetime options.

I'm working on this on my free time, and will post a patch when I have something close to this functionality.