FeTS Challenge 2022: Task 1

[psfoley]

This PR:

• Uses the new FeTSChallengeTaskRunner implementation
• Adapts the Custom Aggregation Functions to use a writable dataframe (i.e. for easy storage of metrics / globals)
• Updated references to FeTS 2022 Training/Validation Data
• Convert jupyter notebook to a script (for easier submission reproduction)
• Tensorboard support and integration

Steps required before merge: [ x ] - Flag to skip Hausdorff 95 metrics [ x ] - Additional testing of code on CPU / GPU [ x ] - Final verification of FeTS Challenge plan parameters [ x ] - New aggregation function interface examples [ x ] - Bring documentation up to date

Improvements to expect after merge: [ ] - Launch collaborator's in their own process for faster training

[sarthakpati]

Converting to draft till ready for merge.