Move model database tables to its own package

Document, NamedEntity and Annotation database tables are moved to its own
"database" package in "*.models.database". It makes model class files smaller,
and more coherent since they do not mix model definition (logic) and database
table definition (persistence) in the same file.
Disable Ebean and Global object, update Play-Slick

Application.conf is modified to reflect the latest change in package
organization (moving database table definitions to "*.model.database"), and
removed the Global object and Ebean configurations since they are not used (at
least at the moment).

Fixed MySQL driver misconfiguration and removed Router configuration since the
default one will be used 'conf/routes', and it gives some problems if something
is left there.

Also added empty routes configuration in 'conf/routes'.
Update README information

Updated README.md to show information about what this repository is about. Will
be updated with more information as the project progresses.