Workout Details & Caching/Serialization for trainee & workout data.

Adds
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  - Serialization/Caching works for trainee and workout data. Tested on S4 in airplane mode, and on VM emulator.
  - Redid workout detail layout. Added 'Results' and 'Description' sections.  

Changes
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__APIHandler__
  - APIHandler is now a singleton. 
  - All APIHandler request methods now throw an IOException, so make sure to catch it when you make the call. (Sorry, I needed it for caching.)  

__Workout__
  - Now displaying 'grade' in workout schedule and workout detail for completed workouts.

__Trainee__
  - 'Notes' on trainee detail pull live from db now.  
  - Replaced 'last workout date' with 'email' in trainee detail.  

Fixes
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  - Workouts don't keep getting added to the workout history. Also fixed a small layout problem with the completed workout layout.