ART: Key-Value Store in Oat header

Allows the storage of string-string pairs in the oat header. The
first significant use of this is storing the implicit-check flags,
so that an oat file can be rejected if it doesn't agree with the
current runtime.

Bump the oat version as the header structure changes.

Change-Id: I15a1c16886e6b8fa7b881c918c19c1efa5c7c00f