Work-in-progress global stats calculation

We want to display global stats on the homepage, such as the total number of registered accounts, total number of executed orders, etc. Calculating these stats requires iterating over some large tables in the database, so we need to cache the values that are computed and only re-compute them every so often.

I added some additional logic into the cron job that is already firing about every 1 minute. The logic checks the values table to see when the last time the global stats were calculated. If they were calculated >10 minutes ago, the code will fire off the stats calculations queries, and then write the values into the values table.

The problem I am hitting right now is that `OrdersModel->calculateOrderStats()` is returning an object like this:

```
array(12) {
   activeBuyCount => 2.0
   activeBuyBTCSum => FALSE
   activeBuyUSDSum => FALSE
   activeSellCount => FALSE
   activeSellBTCSum => FALSE
   activeSellUSDSum => FALSE
   executedBuyCount => FALSE
   executedBuyBTCSum => FALSE
   executedBuyUSDSum => FALSE
   executedSellCount => FALSE
   executedSellBTCSum => FALSE
   executedSellUSDSum => FALSE
}
```

But when I call `->dump()` instead of `->fetchField()` it correctly shows the values calculated. I tried calling `normalizeRow()` (http://api.nette.org/2.0.14/Nette.Database.Statement.html), but that didn't seem to help.

My next steps at this point are:
1. Figure out the problem described above so that the calculated values are returned correctly.
2. Write those values into the `values` table
3. Change the homepage to display these values.

Test Plan:
Visit /api/cron
Merge pull request #3 from MattFaus/master

Add Total field and calm-down the confirmation dialog on New Orders page
Add global stats to the homepage

I resolved the previous issue with some advice from Tom, which means that all of the global stats values are not properly being computed. I added some code to route these through to the homepage and display them, but that will only work once the cron job has fired.  This shouldn't be too big of a deal on production since the cron job constantly fires.

If memcache is available, caching the global stats there would be ideal.

Test Plan:
Visit /api/cron, to make sure the values are populated
Visit the logged out homepage to see stats displayed there
Merge branch 'global_summary'