Make object default values available via its prototype

[nikku]

We should have a general solution that allows us to model default values.

This should fix issues addressed in #9 and allow a consistent access to default values from javascript and during serialization.

Example

var foo = moddle.create('foo');

// accessing default value via prototype
foo.someValueWithDefault; // 'BAR'
foo.hasOwnProperty('someValueWithDefault'); // false

// accessing actual value
foo.someValueWithDefault = 'FOOBAR';
foo.hasOwnProperty('someValueWithDefault'); // true

// removing actual value
delete foo.someValueWithDefault;

Notes

• Some values such as collection properties must not be removable and cannot be provided via the prototype either