Add swipedown exit fullscreen feature

[Ortes]

[codecov[bot]]

Codecov Report

:x: Patch coverage is 0% with 10 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 43.60%. Comparing base (d228479) to head (0974735). :warning: Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/src/chewie_player.dart	0.00%	10 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #930      +/-   ##
==========================================
- Coverage   43.84%   43.60%   -0.25%     
==========================================
  Files          21       21              
  Lines        1601     1610       +9     
==========================================
  Hits          702      702              
- Misses        899      908       +9     

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[diegotori]

Two things:

1. You need to make this configurable from the ChewieConttoller. In other words, you need to make this opt-in.
2. When making this configurable, you also need to make the threshold dismissing on swipe a configurable value, defaulting to a reasonable value.