Adding type hints to class methods returning self and child

[otherJL0]

• Adding SessionDict, WindowDict, and PaneDict type aliases to common.py for _list methods
• Adding hints for methods returning self and collections of children

[codecov]

Codecov Report

Merging #361 (fcfeb39) into master (c30da96) will increase coverage by 0.09%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #361      +/-   ##
==========================================
+ Coverage   87.90%   87.99%   +0.09%     
==========================================
  Files          15       15              
  Lines        1496     1499       +3     
==========================================
+ Hits         1315     1319       +4     
+ Misses        181      180       -1     

Impacted Files	Coverage Δ
libtmux/common.py	87.12% <100.00%> (+0.19%)	⬆️
libtmux/pane.py	82.35% <100.00%> (ø)
libtmux/server.py	79.31% <100.00%> (+0.11%)	⬆️
libtmux/session.py	81.43% <100.00%> (ø)
libtmux/window.py	84.84% <100.00%> (+0.51%)	⬆️

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[otherJL0]

@tony I appreciate the invitation! I don't know if I'll have availability to collaborate simultaneous on Saturday but I'm happy to help gradually add type hints when I can.

[tony]

@otherJL0 Absolutely, open up a PR / issue / discussion whenever you have free time. We are below < 1.0 so there is flexibility to make changes.

You will #359 commit in 0.11

[tony]

LGTM