Process message from parent window

[mwu2018]

The branch next is for the development of v8 terriajs using mobx. Currently the v8 terriajs development is focused on core functionalities and some of the non-core features are ignored. E.g. there lacks of message processing support in the current v8 terriajs. Therefore the line is commented out.

This ticket requires the message processing capability. Once v8 terriajs adds the message processing support, the above line should be uncommented.

[soyarsauce]

Address in fork via https://github.com/TerriaJS/terrace/issues/141