Updated react-tools dependency to be ~0.5.0, updated plugin version to b...

Updated react-tools dependency to be ~0.5.0.  The current version of react-tools as of this writing is 0.5.1.

Updated plugin version to bt 0.5.0 to make it easier for users to stay with 0.4.x if they choose.

I think this is probably a good idea to match the major/minor version of this plugin with the major/minor version of react-tools, as it makes it more clear in the packages.json what the true dependency is.  It looks to me as though that was already the intent, but I thought I would mentioned it again for anyone else who stumbles across this.