removing fiftyone as a hard dependency

[FraPochetti]

• Removed fiftyone as a hard dependency. Needs to be installed separately now.
• Added disclaimer to fiftyone notebook about Colab incompatibility.
• Made sure every notebook installs from pypi and not from master.

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Codecov Report

Merging #1055 (f0f9a60) into master (411101d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1055   +/-   ##
=======================================
  Coverage   85.96%   85.96%           
=======================================
  Files         283      283           
  Lines        5941     5943    +2     
=======================================
+ Hits         5107     5109    +2     
  Misses        834      834           

Flag	Coverage Δ
unittests	85.96% <100.00%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
icevision/data/__init__.py	100.00% <100.00%> (ø)

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[ai-fast-track]

Thanks a lot, @FraPochetti!

[Zubair2019]

• Removed fiftyone as a hard dependency. Needs to be installed separately now.
• Added disclaimer to fiftyone notebook about Colab incompatibility.
• Made sure every notebook installs from pypi and not from master.

Have you checked which models are added when installing via PyPi? Last time I checked there were just a few models in the mmdet directory. Please check.