Summary:
This PR adds a contentInsetStart and a contentInsetEnd property to ToolbarAndroid, allowing offsetting Toolbar contents to different keylines
Closes https://github.com/facebook/react-native/pull/4699
Reviewed By: svcscm
Differential Revision: D2759294
Pulled By: mkonicek
fb-gh-sync-id: f22aa255f07929ad7a99ac7568981d35e848065b