Isaac/snapshot api

Various fixes and improvements to snapshot API.

Things fixed, added:
- [x] Improve snapshot tests to actually verify if events are not being plotted when asked not to (it doesnot cover the case when there are no events, but it catches a bug we've been having with no event query request)
- [x] Fix bug in building no even query request (Issue #99)

Planned to be fixed:
- [ ] by host query do not work