Display expired/missed tickets in /vsp table.

[jholdstock]

:warning: This should not be deployed before decred/dcrwebapi#180 and all VSPs are running vspd >=1.3.0

[xaur]

Nice! I have some ideas:

1. Missed % column is much more interesting than Expired % (which should converge to 0.5% iirc), is Expired % useful on this page?

2. How about renaming Voting to Live for consistency with e.g. dcrwallet outputs? (unless "Voting" is commonly used now in UIs, not sure)

3. How about also exposing block height? Last Updated is "when we got last response from the VSP" regardless of its status, while block height clearly shows if it's stalled or on current chain tip. Personally I find block height more useful for choosing a VSP, if it has stalled it may not vote my tickets. Perhaps height could replace Last Updated alltogether.

[jholdstock]

1. Good point. For the same reason, the absolute number of expired tickets is probably not a useful metric either. I'm tempted to remove that too, what do you think? It'd probably make the table easier to parse.
2. vspd uses "Voting" as a distinct term because it includes both immature and live tickets. I'm fine with using "Live" here though for consistency/simplicity - will update.
3. I don't think just displaying the block height is useful unless it has some extra context - eg. what is the correct block height meant to be? It isn't easy to parse a column of very similar 6-7 digit numbers and know which ones are correct/incorrect. I think it would need some extra design elements. We can do that as a separate change if it is deemed worthwhile.

[xaur]

1. Yes I'd remove it. Missed and Missed % will essentially replace Revoked and Revoked %. Not having too many columns is good too. If the need fir Expired arises it can be added back.

2. Ah I didn't know tha "Voting" includes immature. I suggested "Live" because it sounds easier to understand (like they are "up" or "online", and also not "voting" right now but rather waiting when they can vote). I don't mind either now.

3. "what is the correct block height meant to be?" - I think 1-2 numbers not matching the other 13 would be enough to alert the user to check something else without even knowing what "block height" is. Maybe a "Check the latest block at the block explorer" link would be enough. But yeah this can be done in another PR.

[jholdstock]

Updated with suggestions

[xaur]

Nice! Another small thing is Age -> Launched may read a bit better. Not blocking this PR ofc.