TWEAK: Increase tag and channel max length
TWEAK: Increase tag and channel max length

The max lengths were increased as:

1. Tags could be used to reference a listing
2. Channels could be used to reference a store or listing

This length gives us more than enough space if IPNS addresses increase beyond what they are now. 
OpenBazaar/openbazaar-go,OpenBazaar/openbazaar-go,gubatron/openbazaar-go,gubatron/openbazaar-go,OpenBazaar/openbazaar-go,gubatron/openbazaar-go