Allow option to autodetect new properties in existing models and add those columns in the database.

[jedld]

Allow option to autodetect new properties in existing models and add those columns in the database.

There are times when you need to add a new property to a model and the corresponding column in the database. It would be nice if sugar would detect new columns during a version upgrade.

Though it is achievable now by manually adding the new columns in a migration sql file, there is problem when it is a new installation.... the new columns get created by the schema generator, unfortunately the migration files are also run which causes a duplicate column error.

[whoshuu]

References #151.

[sibelius]

fixed with #328