* Remove global cache variable.
Rather than maintaining cached data in a global variable, instantiate a cache struct and keep it in the `Server` struct.
* Store net params in RPC clients.
This means net params only need to be supplied once at startup, and also removes a global instance of net params in `background.go`.
* Remove static cfg values from GUI cache.
Theres no need for these values to be copied into the cache when templates could simply access the config struct directly.
This also changes the cache accessor so it returns a copy of the cache rather than a pointer, which removes a potential race.
* Rename and move cache.
Cache code was previous in `homepage.go`, but its used in multiple places and not just on the homepage. Its enough code to go into its own dedicated `cache.go`.
* Add network proportion to homepage and /vspinfo.
Proportion is calculated using the number of tickets currently registered with the VSP, divided by the total size of the network ticket pool as reported by `getblockheader`.
The value will only ever be an estimate because:
- it's possible for a single ticket to be added to multiple VSPs.
- vspd does not distinguish between immature and live tickets, whereas `getblockheader` only reports live tickets.
- `getblockheader` is reporting the size of the ticket pool as of the previous block, not the current block.
* xaur suggestions
* Show missed ticket %, not just the raw number.
