Add $IS_DEBUG to allowed values for dev console
Add $IS_DEBUG to allowed values for dev console

Setting the value of EnableDeveloperConsole to $IS_DEBUG will make the
value of this setting follow the value of the debug mode, which is set
during the build. This way, it is not necessary to edit config.xml when
building debug and production apps.

eclipsesource/tabris-js,eclipsesource/tabris-js,eclipsesource/tabris-js