new block column: uniswap prices

[lithp]

• the user somehow specifies which pools they would like to watch, such as ETH/USDC
• when showing the block list do some eth_calls to figure out the price as of each block
• in the future, generalize this to any eth_call users might want to track the result of?

[lithp]

This has a couple components:

• add support for reading from configuration files
• read new column definitions (addresses and calldata) from the configuration file (this might be a partial solution to Address aliases? #13)
• fetch per-block results from the provider
• cache the results in sled