centralize record uuid generation in preparation for further changes
first step towards a more effecient uuid variant - inline the relevant code
and remove the rfc/version marker, as this isn't complying to the spec anymore

side note: this is about a factor of 4x faster than calling uuid.uuid1().hex

bugzilla #843013
reorder bits, to start with node id and then time in natural order

this distributes data from different nodes into different buckets, but keeps
data from the same batches close to each other increasing data locality
improves bulk indexing to a local sqlite on an SSD by about 15% - likely more
on non-ssd mysql (will validate that)

bugzilla #843013
use a 24 bytes long url-safe base64 encoding of our uuids

bugzilla #843013