Community Suggestion - HF20: Out of RCs can't power up

[TimCliff]

With the new implementation of RCs in hardfork 20, it is likely that many users will have insufficient RCs to transact as much as they want. When users run out of RCs, they are currently stuck until their RCs recharge or they power up more STEEM.

It is currently difficult to power up more STEEM for most users, since powering up requires RCs. Users have the option to use the BlockTrades.us interface (which supports the purchase of Steem Power directly) but users who rely on the other exchanges (such as Bittrex, UpBit, etc.) or already have the STEEM they want to use sitting in their account do not have this option.

If it is not too technically challenging, I suggest the following:

• [ ] Define a new DISCOUNTED_POWER_UP_WINDOW
• [ ] Define a new DISCOUNTED_POWER_UP_RC_COST
• [ ] Define a new DISCOUNTED_POWER_UP_MINIMUM
• [ ] Allow users to power up STEEM at a discounted RC rate once per DISCOUNTED_POWER_UP_WINDOW by only having to pay DISCOUNTED_POWER_UP_RC_COST, provided they power up at least DISCOUNTED_POWER_UP_MINIMUM STEEM.

Suggested values:

• DISCOUNTED_POWER_UP_WINDOW: 12 hours
• DISCOUNTED_POWER_UP_RC_COST: 0 RCs
• DISCOUNTED_POWER_UP_MINIMUM: 1 STEEM

[iamsmooth]

Idea from @roadscape to allow RCs to go negative in the specific case were the operation is a power up and RCs return to positive after the power up.

[roadscape]

To clarify -- a simpler approach might be to allow pushing ops that would generate enough RCs to cover themselves (when RC level is otherwise too low pre-op). The main use case is for transfer_to_vesting but could apply to delegate_vesting_shares when undelegating in an RC crunch.