Nginx wait for full start. Split julia pkg instal.

- Added check in host nginx to wait till both tornado and nginx in container have started up.
- Split Julia package installation while creating docker image. Easier to recover from a failing package. Some of the packages can be pretty heavy.
persist sessions and refactor code:

- persist (stopped) sessions for all users.
- refactor of host python code.
Merge pull request #15 from tanmaykm/tanmaykm

persist sessions, wait for container to load fully, fixes and refactors