Unify block gas limit and size limit

[rafoo]

I think that you already suggested this about a year ago:

Should the block size limit be folded into the gas limit?

There are currently two limits that apply to blocks: a size limit and a gas limit. The role of the gas limit is to ensure that the validation of a block can be completed fast enough for a node to follow the chain and the role of the size limit is to ensure that the blocks do not consume too much bandwidth and disk space. As a result, bakers need to solve an optimization problem based on two constraints when including transactions (a two-dimensional knapsack). Blocks currently less than full, th…

IIUC, you propose to:

• make some reasonable assumption about the speed of the internet connection of Tezos nodes,
• charge some extra gas in each operation, proportionally to the size of the operation, to account for its participation in downloading time,
• raise the gas limit per operation (because the previous gas increase should not invalidate any currently valid operation),
• raise the gas limit per block by the same factor,
• drop the size limit per block,
• keep the operation size limit untouched.