Full plumb through of Session support. Also fixed some test issues
- Load session and get necessary information in kernels list
- Run Cell button now works as expected
- Added a ToggleAction base class which can be used for anything that switches icons. I'd still prefer to have this be dynamic and as clean as the extension classes
- Fixed account test unhandled promise rejections (caused by incorrect / invalid tests) that made it hard to see all the test run output.
* Initial toolbar work
- This is in-progress and needs additional fixes
* Resolve PR comments
* Added empty kernel and hook up with Kernel dropdown
* Resolve PR comments
