Update the version of ReactXP

[Inei1]

The frontend currently uses an old version of ReactXP, version 0.42.0-rc.22. One approach to fixing #5 is to get access to the requestFocus() and other focus methods for text inputs. The version history states that requestFocus() was added in Version 1.1.2 rc-2 of ReactXP, so this or any later version, such as 1.3.0, should be good enough. The breaking changes in newer ReactXP versions do not break anything in the frontend.