feat: Dark Theme (#131)

* refactor: Add DarkTheme, new colors in theme & update components to use it

* chore: Remove 'console.log' statements

* chore: Change dark theme property from string to boolean

* feat: Add ability to toggle the theme from the drawer

* fix: Wrap typography example screen with 'withTheme'

* style: Update components to use correct dark theme colors

* style: Update dark theme primary color and rn-navigation toolbar now gets the color from the theme

* style: Add color prop to DrawerItem and update the example

* style: Change the unchecked color in both Checkbox and RadioButton

* chore: Add `yarn-error.log` to `.gitignore`

* chore: Use lodash instead of lodash.merge

* chore: Address PR comments

example/src/TextExample.js

@@ -8,14 +8,16 @@ import {
   Paragraph,
   Subheading,
   Title,
+  withTheme,
 } from 'react-native-paper';
 
-export default class TextExample extends Component {
+class TextExample extends Component {
   static title = 'Typography';
 
   render() {
+    const { theme: { colors: { background } } } = this.props;
     return (
-      <View style={styles.container}>
+      <View style={[styles.container, { backgroundColor: background }]}>
         <Caption style={styles.text}>Caption</Caption>
         <Paragraph style={styles.text}>Paragraph</Paragraph>
         <Subheading style={styles.text}>Subheading</Subheading>
@@ -28,8 +30,11 @@ export default class TextExample extends Component {
 const styles = StyleSheet.create({
   container: {
     padding: 16,
+    flex: 1,
   },
   text: {
     marginVertical: 4,
   },
 });
+
+export default withTheme(TextExample);