Updates for the installer (hopefully the last ones)

1.7.2-dev.json: The installer will read all the libraries and download them when needed. This also contains links for libraries that arent donwloadable from libraries.minecraft.net.

BLVersion.properties: This will be shipped with BlazeLoader and will make it possible for the installer to be able to work if there is a new version of minecraft/MCP (except if something drastically changes).

I hope this will be the last PR i have to make for the installer as i'm getting close to a beta release for the MCP install.