Pin small transactions

[mitar]

Currently we pin (in IFPS) only block, so everyone participating in the blockchain will have a copy of all blocks. But if data pointed to by transactions is not available (disappears from the network), then this makes the blockchain itself less useful. We do not want to simply duplicate everything anyone references from a blockchain, but we could maybe have some small limit and all transactions which are smaller that the limit could be pinned by everyone. (We can know how bit is data pointed to by transactions so we can check that easily.) We could even allow users to decide what is this limit. And for other bigger data, we could have less duplication across the network, with less redundancy. Maybe people could participate in byteswap for those larger transactions.