Added numericality validation for grade field.

signed-off-by: Pedro Scocco <pedroscocco@gmail.com>
Added unit tests for presence and numericality.

signed-off-by: Pedro Scocco <pedroscocco@gmail.com>
Fixed acceptance test for invalid grade

Signed-off-by:Pedro Bruel <pedro.bruel@gmail.com>
Added acceptance test for non numerical grade.

Signed-off-by: Daniel Miranda <danielkza2@gmail.com>
Signed-off-by: Pedro Scocco <pedroscocco@gmail.com>
Merge pull request #63 from mezuro/numeric_validation

Numeric validation