Introduce new Context.ANNEX_B flag and move relevant functionality behind this flag

[p-bakker]

As Rhino started out as a port of SpiderMonkey, which was the JavaScript Engine for FireFox, some stuff got implemented that later on got moved in the Annex B of the EcmaScript sepcification, which should only be implemented by browsers and not by non-browser-based JavaScript engines, like Rhino

This case is to introduce the Context.ANNEX_B flag and move all functionality/behavior that is not part of the core EcmaScript specification, but is part of Annex B behind this new flag.

In v2.0.0 this flag should be disabled by default. We could opt to implement this flag alreadt in v1.7.15 and have it set to true by default (if Context.VERSION_ECMASCRIPT is not being used)