Make possible to access macro descriptor when the macro is not saved with programming rights

For personal macros for example to test before an admin save it to provide it to all users.

To support it in velocity (less needed in other languages since they need programming right to work anyway) DefaultWikiMacro#execute needs to put the Map<String, Object> macroContext in the VelocityContext (as well as the context).

To be more clear, having:

$macro == $context.macro