Add Configurable Google API Limit Option

[Sleep-is-Good]

Being able to use and toggle features of the google api limit is great. However, I and I would believe others, don't want to accidentally go over the free tier limit for api calls. It would be great if there was a setting that could be specified in the admin panel that would limit the amount of api calls that TREK will make per day.

When TREK is going to hit this limit, it will stop making requests until the next day. This could be disabled by default (setting of 0 maybe) and for those that want to stay under that limit, they can specific the number of requests they want to allow per day.

[mauriceboe]

Done! Admins can now set a daily limit for Google API calls in the admin settings, with a usage counter for today. When the limit is reached TREK falls back to the free providers until the next day. It ships with the next big update.