Add automatic migrations support

Add a Migrator class and a migrate script to
automatically update database structure with
rpm updates.

Another step forward for continuous integration.

Signed-off-by: Martin Abente Lahaye <tch@sugarlabs.org>
Add migration SQL files

002: Create migrations table and insert 001-harvest.sql
     file, to make sure its never executed.

003: Rename KEYS and CONSTRAINTS to more meaningful
     names. Help to maintain these constraints.

004: Add birthdate and gender as PRIMARY keys to
     learners table. Help identify learners as a
     serial, age and gender unique tuple.

005: Group learners FK columns in instances and
     launches tables. Help make table definitions
     more readable.

006: Hash existing serial numbers. From this version
     and on, we wont store plain serial numbers, only
     hashed versions.

Signed-off-by: Martin Abente Lahaye <tch@sugarlabs.org>
Update insert SQL

Update data parsing and SQL statements, according
to the tables structure changes.

Signed-off-by: Martin Abente Lahaye <tch@sugarlabs.org>
Include mime_type metadata

Signed-off-by: Martin Abente Lahaye <tch@sugarlabs.org>
Release 0.2.0-1

Signed-off-by: Martin Abente Lahaye <tch@sugarlabs.org>