Fixes #868, panic on upgrades.

This was a problem with 0.7.x upgrades to 0.8 where there was a raft snapshot. The recovery method assumed certain structures would be there and they weren't.
Merge pull request #897 from influxdb/868-panic-on-upgade

Fixes #868, panic on upgrades.
Format
Update the changelog
Get rid of migration
Remove some api endpoints that are redundant
Some cleanup
Api should have it's own coordinator interface
Don't overuse interfaces if there's no benefit
Use GetQueryString() instead of accessing the internal field
Fix parsing of multiple queries

Fix #885
Use the client instead of manually posting to the server
Get rid of the unnecessary extra argument
Remove some cruft
Use separate file
Remove an unused interface
Move permission checking to permissions
Split the different engines in their own types
Get rid of the explain query tests
Fix the some integration tests