private mathhub no library

[kohlhase]

continuing from #9:
When installed, http://localhost/#/library gives me Failed to load library.
And this is not surprising, since it does not know about a library yet.
As most of the users of private MathHubs have a previously installed local MathHub, ./configure should ask for that (probably pick it up from a pre-existing MMT system implementation) and use that.