maxipatch for support of multiple DBs.

maxipatch for support of multiple DBs.

new 3 different kind of BD can coexist:
user) the user db, where his stuff is stored
   tables are named foo_user
library) the library db, a read only database where the standard library should be
   installed and that is the target of the publish act
legacy) a legacy database (not mandatory) where really read only data is stored

every db can be implement with an sqlite file or a mysql database.

the default configuration file sets 1 and 2 to be the mysql matita database on mowgli,
thus nothing should change for mowgli users. database 3 is not used if you are on mowgli.

the way it should be used by matita users out of the unibo network is commented in the config file:
1) file://~/.matita/user.db for his development
2) file:///usr/share/matita/metadata.db for the matita precompiled standard library
3) mysql://mowgli.cs.unibo.it for the legacy coq stuff, both queries and xml are fetched trough
   the net

this allows us to really distribute matita in a rather sane way, with a
precompiled library visible systemwide and having all per user data and
metadata in ~/.matita. There is no need for the user to install and configure
mysql, and can use mowgli just decommenting few lines in the config file.