Add ability to use to use metric and/or imperial system (#66)

* Add ability to use to use metric or imperial system.

* Add ListChoiceDialog and handle default unit system setting.

* ListChoiceDialog scrollable prop.

* Add weight_unit to WorkoutExerciseSchema and show and save weight in kg or lbs depending on default unit system setting.

* Make edit sets with paper form work with lb.

* Change default + and - weight and reps buttons.

* Detect default unit system by country on the first time app is installed.

* Add unit tests for kg vs lb.

* Add snapshot-diff and test to compare max sets vs normal sets.

* Add unit tests for edit sets with controls for kg vs lbs.

Author: ferrannp

.flowconfig

@@ -37,6 +37,7 @@ node_modules/react-native/Libraries/react-native/react-native-interface.js
 node_modules/react-native/flow/
 node_modules/react-native/flow-github/
 node_modules/react-navigation/flow/react-navigation.js
+flow-typed/.*
 
 [options]
 emoji=true

config/setupTests.js

@@ -5,6 +5,13 @@
 import Enzyme from 'enzyme';
 import Adapter from 'enzyme-adapter-react-16';
 
+const snapshotDiff = require('snapshot-diff');
+
+const { toMatchDiffSnapshot } = snapshotDiff;
+
+expect.addSnapshotSerializer(snapshotDiff.getSnapshotDiffSerializer());
+expect.extend({ toMatchDiffSnapshot });
+
 Enzyme.configure({ adapter: new Adapter() });
 
 // We never want to call the real methods of this module (or bad things are going to happen)