### Motivation
The ref function is called twice on updates (see https://reactjs.org/docs/refs-and-the-dom.html#caveats-with-callback-refs). This behaviour causes the variable `this._manager` sometimes to be null during rendering and in that case actions are pushed to the queue again. Since the queue is only processed once (during componentDidMount), somes changes will never be visible. The simple solution is to bind the ref-function as mentioned in the link above.
### Test plan
Dynamically change `visible` parameter of Modal. The Modal won't be visible on the second time.
* 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
