Properly autoload on keys which are namespaces + optimisations

o Remove decoration of template fwd declarations which happen in
rootmaps as they are not useful anymore. Indeed we fwd declare
w/o using any default parameter. This fix reverts these 2 commits:
3f0aff953f4f376ed7aa119ebf196c1856cb3511
c04ca87044b42e2496cfb4fb4295584f9336ae65

o Rootcling generates even more expressive rootmaps, not only with
class and namespace specifiers, but also typedef. E.g.
[libA.so]
class A
namespace NS
typedef TD

o TCling reads rootmaps with less string comparisons.