Remove DEFAULT_FEE, add temporary acceptance of too-small per-kb fee >= ...

...0.1, denominations based on DEFAULT_DUST_THRESHOLD, document fee arg to create_transactions as unused, se DEFAULT_DUST_THRESHOLD for wallet dust collection instead of calcualted tx fee

Includes various clean up issues for per-kb and temporary exception for compatibility with old wallets. 

Has been tested on testnet but can use some more.