MachineAdmin: Add `onClick` method to get an image.
MachineAdmin: Load thumbnail image from Gallery
MachineAdmin: Refactor `MainActivity`

Refactor `LoaderManager.LoaderCallbacks<Cursor>` methods to
`ImageLoader` class.
MachineAdmin: Create library project for shared code
MachineAdmin: Refactor `MachineTabListener` to library project

Refactor `MachineTabListener` to more general `FragmentTabListener`. Add
it to a library project in order to reuse it between ExerciseMachines
and MachineAdmin.
MachineAdmin: Add tab navigation
Add SmartImageView JAR file
Stub out "Add Category" menu item
MachineAdmin: Add category activity
MachineAdmin: Add menu with "Save" item to `CategoryActivity`
MachineAdmin: Get thumbnail for category
MachineAdmin: Differentiate machine and category name labels
MachineAdmin: Save categories using Parse
MachineAdmin: Save machine data
ImageLoader: Only need a Context, not an Activity
Move menu processing from `MainActivity` to `DetailsFragment`
Create Category object
Machine class
Make tab for adding categories
Use Picasso to load images