Add support for coded QNames/AugmentationIdentifiers

Add support for coded QNames/AugmentationIdentifiers

Profiling is showing we are spending about 46% in readQName(),
which further breaks down to 30% in readCodedString() and 61%
in QNameFactory.create().

Out of 1.7M invocations of readQName(), we end up loading only
508 QNames -- which is understandable, as the number of QNames is
bound by the SchemaContext contents. This also applies to
AugmentationIdentifiers.

This patch defines a new streaming format version, which uses
the same linear coding approach we take for Strings, taking
hash-based lookups out of the hot path -- bringing reconstruction
time down from 36 to 19-24 seconds.

It has also the effect of reducing the snapshot size, in our testing
bringing a 388.8MiB snapshot down to 210.6MiB.

JIRA: CONTROLLER-1898
Change-Id: Ibbc96c286d52b3261b04dd7de02e13bc6b44e803
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>