Add estimated monthly usage

[willgarrett64]

This ticket is just a suggestion for us to discuss. It might be nice if somewhere we could display what we estimate the monthly bill to be based on current usage.

For Servers/DNS, I image we can just calculate how long is left in the month and multiply this by the cost of the current services. Then add this to the current monthly usage. CDN is probably trickier since it's based on usage rather than a set cost per unit of time.

As I say, just an idea to discuss if we even want/need this before getting into too much detail of implementation.