Splitting dashboard calls up instead of using one single API call:
* Use getuserbalance for Balance updates
* Use getuserworkers for Worker updates
For those and potential other SQL intensive Ajax calls I have added a
long ajax refresh interval setting. It can be set via admin panel and
will change the refresh time on the JS file on the dashboard for those
two calls.
Should help a bit with high worker and transaction volume pools.
Address #1159
Allows pools to disable the dashboard and dashboard API completely.
Useful if you are not running a master/load(/load/load) setup to deal
with frequent live queries.
Fixes#876 once merged.
