User must click "Save" on Intervals screen to make intervals work

Hi,
I was cursing the name of this module's author all evening, until I realized the module works as intended and the problem I was having was simply that nowhere in the documentation does it mention you have to click the "Add" button on the Intervals page.

Although this is really stupid from a UI perspective (Don't make it look like a config form has default values when those values require an action to activate!), probably half the users who simply think this module is non-functional are experiencing what I did — I.e., any user that can't figure out why the "Refresh stats" page doesn't show anything and appears to hang.

Probably a better long-term solution would be to make those values actually default values — install them by default, let the user remove them if he or she dislikes having that level of granularity.

See attached patch for documentation.