latest gxp for better Mareano integration

This pulls in 2 very minor changes in GXP to make it possible before the Mareano application to inherit easier from GeoExplorer:

https://github.com/boundlessgeo/gxp/pull/222
https://github.com/boundlessgeo/gxp/commit/0ec32bbef654c23dd67e268c4345bab0c7b2de6a