readability for intoConstructors transformer
better encapsulation in constructors phase
separation of concerns: guard non-specialized ctor-stats in constructors

This commit modularizes TemplateTransformer by moving two methods
from TemplateTransformer into the newly added OmittablesHelper.

The methods in question are:
- mergeConstructors(genericClazz, originalStats, specializedStats)
- guardSpecializedInitializer(stats)

That way, the rewriting that introduces a guard for the execution of
non-specialized ctor-statements is encapsulated in
trait GuardianOfCtorStmts.
skipping trips to specializeTypes when not necessary in constructors
Golfed about 20 lines into the sand trap.

And it's a nice golf clinic and all, but let's remove our
golf gloves and take in some film.

  for (stat <- defBuf.iterator ++ auxConstructorBuf.iterator)

A quick count:

 - defBuf is a ListBuffer (1 mutant)
 - auxConstructorBuf is a ListBuffer (2 mutants)
 - two mutable iterators over mutable sequences (3, 4 mutants)
 - Iterator.++ joins them and is BY-NAME (4 mutants, 1 tragedy in waiting)
 - the joined Iterator is a new mutable structure (5 mutants, now 3 deep)
 - omittables is a mutable Set (6 mutants)
 - the 5-layer-3-deep iterator mutates omittables as it walks

[The following is a public service breakdown. The letter
sequence y-o-u is a local variable which should be replaced
with your name, whoever "you" are, if you commit any code in
these parts.]

Hear my plea! YOU DON'T HAVE TO DO IT THIS WAY! It isn't simpler,
faster, easier, more satisfying, shorter, more pixelated, there
just isn't any advantage to it, even if you're lazy! Especially
if you're lazy! Whatever combination of virtues and vices exist
in your personal petri dish, this will never be a hilltop!

PLEASE COME ENJOY A DRINK WITH ME AND MY FRIEND 'VAL' !!
I'LL INTRODUCE YOU! I THINK YOU WILL REALLY LIKE HER! I HOPE
YOU WILL SEE A LOT OF ONE ANOTHER! REMEMBER THAT NAME, 'VAL' !!
SHE'LL HAVE HER EYE OUT FOR YOU!