Added license, adjusted comment
Added AssociationProperty::getAsEntity()
Added methods to modify collection
Added save() and delete() methods for Entity
Renamed empty() to isEmpty() as empty seems to be a keyword
rename isEmpty() to clear()
Added getter for identifier names, fixed types in doc blocks
Fixed docblock for constructor
Fixed docblock for getColumn()
Added Entity::setColumn(), that sets the value of the column back to the
entity
Added Entity::getIdAsStr()
Added Entity::getDoctrineAdmin() getter
Added AbstractProperty::setValue() to set a value of a property
Added ScalarProperty::setValueFromString() to set a value from a string