* 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.
* Ensure purchase height set for confirmed tickets.
* Show purchase height in admin screen.
Only show purchase height when the ticket is confirmed, because if a ticket is not confirmed, its purchase height is not yet known.
