Add launcher repository config file location to boot properties.

Allows users to configure whatever remote repositories they want
via a global config file shared between sbt and activator.

Fixes #114 


Review by @jamesward   

Note: See http://stackoverflow.com/questions/19410860/how-to-configure-typesafe-activator-a-priori-to-use-an-existing-local-maven-re/19494548#19494548