[sqllab-presto] adding partition information

[mistercrunch]

Showing latest partition information as a header in the TableElement component, plus a "copy to cilpboard" icon to get a query to get detailed information about existing partitions.

Side-missions:

• a new abstraction to provide per-database-engine extra table metadata, this runs async and independently from the common table metadata endpoint to avoid slowing down showing the column/type info to users
• my first mochajs unit tests, I had to play some small tricks here to decouple my component from react-redux for the react tests to run
• overdue rename of SqlEditorTopToolbar to SqlEditorLeftBar
• a bit of refactoring in the python tests
• a very basic python test, just making sure the endpoint works, no Presto mocking or anything fancy there
• minor cosmetic touchup of CopyToClipboard component to allow a node in the tooltip and removing unwanted  
  
  

@bkyryliuk @ascott

[mistercrunch]

ping!

[mistercrunch]

I'm going to babysit this one in staging