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
Disable the test because of a missing file in #861
Add some logging
Simplify the response types
Add profiling endpoints to the http api
No need for a function variable
Write to the buffer instead of using append