Rewards of bridged $NEO tokens

[gsmachado]

Imagine the following scenario:

• User deposits $NEO to the bridge contract on N3
• User receives $NEO on the Neo X

Ok, what happens with the $GAS rewards of the bridged $NEO tokens on N3?

[mialbu]

This is still a discussion point. However, in order to prepare a bit until this question is answered, I have added a storage value that will track the amount of $GAS that's been sent to the contract due to $NEO token holdings (i.e., $GAS payments with from being null). This way, it'll be easier to add a feature that manages the distribution of GAS in a future version of the contract, also considering the already collected $GAS rewards from holding $NEO.

See the neoHoldingGasRewards() function in PR #138.