allow NN to be filtered/redefined for NN

there been examples of auto aggregation of NN be a hit or miss for how much it makes sense in the release.

For example:
Beta1: Added a few components to the Ionic Palette: <c1> <c2> <c3>
Beta2: Added a few components to the Ionic: <c4> <c5>
Alexey Kazakov: But in the final verision I would like to have: Added new components: <c1>,...<c5>.

One suggestion been to have ability to rewrite the full NN version at final but I just know that will kill us becase it is going to be a pain to copy/paste right.

Alternative suggestion is:

A) during rendering of the "final" aggregation set a asciidoc variable (i.e. "finalnn") allowing us to use asciidoc conditionals like

ifndef::finalnn[]
This piece of news was only relevant for Beta1
endif::finalnn[]

See: http://mrhaki.blogspot.ch/2014/08/awesome-asciidoc-using-conditional.html

B) allow to add a .Final newnoteworthy adoc to use as place to write the aggregated news ..note, these should still be merged with the former NN's. so you only need to write the sections that are actually different.