Doc: update build script with alembic

and integration of fdegomme modifications
Doc: update install script
Sql: uggly fix for schema hangling with alembic

sqlalchemy is not handling schema well and changes the default schema
resulting is wrong look up of the alembic_version table.

explicit set of the default schema before running alembic to bypass this
problem
Doc: add precision for sudo dependency
Doc: corrections after review
Doc: correction after review
build_navitia.sh: change sudo su - login by sudo -i -u login and improve quoting
Doc: don't depend on jormungandr db
Merge pull request #660 from antoine-de/install_update

Install update