Trainee List works with Trainer API, also added APIHandler for  HTTP requests

Description
==========  

+ Bare implementation of trainee list and details activities/fragments. Pulls data from Trainer API.
+ Supports two-pane/landscape orientation.

__Adds__  

+ DRY up code by adding an `APIHandler` class to generate HTTP requests (and later handle responses from the Trainer API)  
+ `TraineeListActivity` loads `TraineeListFragment`, which displays the list of trainees. Right now it only displays the name. Note: The DB is being modified to return trainee Name and ID, but right now it only returns ID, so that's what is being displayed here.  
+ `TraineeDetailActivity` loads `TraineeDetailFragment`. Right now, it just displays the trainee's name in a text view when you click on a trainee from `TraineeListActivity`/`TraineeListFragment`.  
+ `TraineeContent` stores a list of `TraineeItem`s and maps trainee IDs to a `TraineeItem`.  
  + Inner class `TraineeItem`
+ A bunch of xmls.

__Changes__  

+ (Temporarily) changed `mEmail` and `mPassword` in `LoginActivity` to `public static` because I wasn't sure how we planned to store credentials for authorization. We should try to agree on something.  
+ After login, launches `TraineeListActivity` instead of `MainActivity`.

__Removes__  

+ Nothing