Small modification to LoadandCite

I made a couple of small modifications to the function. 

a) Function now uses the same repo as a user might use for `update.packages` by reading the `repos` option in the `.rprofile`. Since many people set their own, this would be good because it defaults to their preferred choice before using the standard one.

b) small modification to check whether the `install` flag is set. Removed some extra code.