ENH: Update session

[Miksus]

This PR has the following changes:

• Now session should be passed to task classes. Else, empty session is created.
• Deprecated session.get_task

[codecov-commenter]

Codecov Report

Merging #79 (9168608) into master (05861b7) will increase coverage by 0.03%.
The diff coverage is 97.91%.

@@            Coverage Diff             @@
##           master      #79      +/-   ##
==========================================
+ Coverage   91.10%   91.13%   +0.03%     
==========================================
  Files          88       88              
  Lines        4339     4366      +27     
==========================================
+ Hits         3953     3979      +26     
- Misses        386      387       +1     

Impacted Files	Coverage Δ
rocketry/core/task.py	93.01% <87.50%> (+0.05%)	⬆️
rocketry/__init__.py	100.00% <100.00%> (ø)
rocketry/application.py	84.21% <100.00%> (+2.12%)	⬆️
rocketry/core/schedule.py	89.65% <100.00%> (-0.35%)	⬇️
rocketry/session.py	91.94% <100.00%> (+0.43%)	⬆️
rocketry/utils/dependencies.py	84.00% <100.00%> (ø)

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