feat: add entry point for returning Celery app

[uniqueg]

Description

• provide method .create_celery_app() for class Foca that returns a configured Celery app
• can be used to avoid issues like circular imports that are likely to arise from the previous implementation
• bumps version to 0.11.0

Fixes #159

[codecov]

Codecov Report

Base: 100.00% // Head: 100.00% // No change to project coverage 👍

Coverage data is based on head (dd20da9) compared to base (1223c64).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff            @@
##               dev      #160   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           20        20           
  Lines          967       974    +7     
=========================================
+ Hits           967       974    +7     

Impacted Files	Coverage Δ
foca/foca.py	100.00% <100.00%> (ø)
foca/version.py	100.00% <100.00%> (ø)

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