core: serialize block major/minor versions as bytes, not varints
core: serialize block major/minor versions as bytes, not varints

This allows them to be saved as a fixed (one byte) chunk whatever
the value. Using a varint will use two bytes as the high bit gets
set.

This is backward compatible with current usage (0-2 values).

ranok/bitmonero,eiabea/bitmonero,eiabea/bitmonero,eiabea/bitmonero,eiabea/bitmonero,ranok/bitmonero,ranok/bitmonero,eiabea/bitmonero,eiabea/bitmonero,ranok/bitmonero,ranok/bitmonero,ranok/bitmonero