Changes to compute preferred controller (goal - prevent flickering of Kernel Status label)

[DonJayamanne]

Proposal for new users (in the following order)

• If python is installed, then wait and create active interpreter controller
• Next create the local kernel specs
• After the above create the following controller in no particular order:
  • Create rest of the controllers after all interpreters have been discovered
  • Create jupyter remote controllers

Proposal for existing users

• Existing code should be fast enough to load all controllers as we load from the cache