[contracts] Review storage deposit pricing (StorageDepositLimitExhausted)

[cmichi]

To reproduce:

• Extract the three contracts from contracts.zip. Those are the ink! master examples built with cargo +nightly contract build (so in debug mode). Latest cargo-contract release (0.17.0).
• Run substrate-contracts-node --dev, I use the latest 0.5.0.
• Upload flipper.contract, erc20.contract and erc721.contract from Alice (the order doesn't play a role).
• The last upload will fail with system.ExtrinsicFailed / contracts.StorageDepositLimitExhausted.
• If I open a new, private browser window and try to upload the third contract there it doesn't work either. I had suspected some UI bug with its local storage, but that doesn't seem to be the case.
• It works if I upload the third contract from Bob.

Alice's balance after starting a fresh node:

transferrable 1.1529 MUNIT

Alice's balance when getting the error (so after uploading the second contract):

1.1516 MUNIT
transferrable 178,455.5042 UNIT
reserved 973,242.0000 UNIT

So seems like it's an issue with pricing the deposit.

Note that there is use-ink/ink#1112, where a user runs into contracts.StorageDepositLimitExhausted as well (though in a different set-up).

[athei]

This is no bug in the contracts pallet as far as I can see it. The math checks out. It is just that the deposit values within the runtime configuration are way too high. 6 units per byte. That is insane. Moved it to the correct repository.