Double-check our gas prices

[cwgoes]

Figure out a moderately coherent strategy for pricing compute & storage operations, answering the following questions:

• Relative price of compute / storage? Do we need an underlying hardware model?
• Should modules building on the SDK calculate their own gas prices or just use the GasKVStore / crypto wrapper functions (is that enough)?
• How much gas does a one-sender, one-recipient, one-coin transfer transaction need (as a relative benchmark)?
• Gas limit should be increased before transfers are enabled (current block gas limit allows for ~10 txs/block). What should be the new gas limit?

Put all gas prices in governance-controlled parameters.

Write this up in a spec doc (=> "Core SDK" spec doc).

[cwgoes]

I think we should construct a basic benchmark (store reads/writes/iteration, expensive cryptographic operations), run it on a node-representative VM (midrange dedicated server?), and use the result of the benchmark to choose gas prices, adding in an extra cost for storage writes due to the persistent disk space requirement.

This should provide a reasonable-enough initial configuration, which governance can vote to change later as necessary with ParameterChangeProposals.

[cwgoes]

Typical node: MacBook 13 inch latest gen. Run on multiple hardware setups, average somehow.

Make sure benchmark is easily extensible.

Benchmark should include overlapping execution, best-fit the results.

[cwgoes]

Also see #1013 (comment), I wonder if we need a scratch space / storage space separation a la memory / storage in the EVM.