Fixed ImportError exceptions in clients where Flask is not installed.

[ethangreen-dev]

Resolves #71

Changes

• Added stochss_compute.api.dataclass module and moved all model definitions into it.
• Added import guard to stochss_compute/api/__init__.py to swallow ImportError exceptions in environments where Flask is not installed. Note that environments where Flask is installed but other server dependencies are missing can cause unintended behavior.
• Adjusted model imports throughout codebase to utilize stochss_compute.api.dataclass.
• Removed stochss_compute/api/v1/dataclass.py
• Removed stochss_compute/api/v1/gillespy2/dataclass.py

[mdip226]

When I tried to run this, I got

Traceback (most recent call last):
  File "app.py", line 1, in <module>
    from stochss_compute import api
  File "/home/mdip/Projects/stochss-compute/stochss_compute/__init__.py", line 1, in <module>
    from stochss_compute.remote_simulation import RemoteSimulation, ComputeServer
  File "/home/mdip/Projects/stochss-compute/stochss_compute/remote_simulation.py", line 10, in <module>
    from .remote_utils import unwrap_or_err
  File "/home/mdip/Projects/stochss-compute/stochss_compute/remote_utils.py", line 6, in <module>
    from stochss_compute.api.dataclass import ErrorResponse
  File "/home/mdip/Projects/stochss-compute/stochss_compute/api/__init__.py", line 6, in <module>
    from .api import start_api
  File "/home/mdip/Projects/stochss-compute/stochss_compute/api/api.py", line 5, in <module>
    from .v1 import v1_api
  File "/home/mdip/Projects/stochss-compute/stochss_compute/api/v1/__init__.py", line 4, in <module>
    from .memory import v1_memory
  File "/home/mdip/Projects/stochss-compute/stochss_compute/api/v1/memory.py", line 1, in <module>
    from msilib.schema import Error
ModuleNotFoundError: No module named 'msilib'

[briandrawert]

We are deprecating Flask, this is not needed