Support @inheritDoc and fix documentation for methods without jsdoc documentation

[cboulanger]

The ApiViewer should support the JsDoc @inheritDoc tag and use the documentation of the parent class (see http://usejsdoc.org/tags-inheritdoc.html) or (extending the jsdoc useage), its qx Interface class.

In addition, the current behavior needs to be fixed where methods without documentation will use the closes comment block even though there are empty lines before the method declaration:

@johnspackman Is that technically possible with the AST? Or do we need to enforce at least a

/**
 * @inheritdoc
 */

before the method?