Adding loading state for predict actions

[anesmemisevic]

:rocket: What

Adds the loading spinner for the in-progress actions. Namely, the server/docker-predict actions. Resolves #237

:computer: How

By introducing the Halo lib for the spinner and implementing a decorator for it.

:microscope: Testing

Tested with methods from test_truss_handle.py in /tests. Tests are passing. ✅

[bolasim]

Thank you so much @anesmemisevic . We'll review today