Summary:
1. Provide forceRTL function for developer to test RTL layout in LTR language bundle in I18nUtil and expose it in I18nManager.
2. Rename `allowRTL` and `setAllowRTL` functions
Reviewed By: fkgozali
Differential Revision: D3663693
fbshipit-source-id: 3db13a44c069ae73d1728c211306422db5dd8122
Summary: create new RCTI18nManager.js to warp-up native module I18nManager and fix current use of it.
Reviewed By: ericvicenti
Differential Revision: D3547427
fbshipit-source-id: 53a695c94ca6bba2f566d0725c553e58d60bf451