Fix data scheme in cassandra writer (#514)
Fix data scheme in cassandra writer (#514)

Fix data scheme so that cassandra stores channel and thing id as
text. Support sorting by time per channel partition.

Signed-off-by: Aleksandar Novakovic <5730e1b08649f92e222ad2d26329a6da6debebc2@mainflux.com>
Mainflux/mainflux-lite,drasko/mainflux,drasko/mainflux,drasko/mainflux