HUE-1805 [spark] Second version with REST Job Server

Async query execution
Select context automatically or create/pick one
Create context
Delete contexts
Upload jar

Todo:
save a script
support result different than a map
add history in navigator
add link to job to open them with their result
parameted editor
consolidate menu bar
default classpath to empty
lot of UX

In Job Server:
more infor from API (to be continued)