Add support for traitlets configuration with major refactoring.

[fleming79]

This is a major refactoring with breaking changes.

Main Changes

• Kernelspecs have changed (should be installed)
• async-kernel commands modified:
  • -a | --add --> install
  • -r | --remove`` -> uninstall`
  • added --help-all, --show-config & --show-config-json
  • main_shell.timeout --> timeout
  • interface.host --> host
  • Added '--user' option to install in the users jupyter directory.
• The interface
• The kernel must now be started from the interface.
• Configuration is done using traitlets configurables.
• subshell_manager is removed
• Subshell class is removed
• Subshells are now separate instances of the subshell_class
• Added BaseShell and IPShell