Multi-signer support

[trmid]

Currently only 1/X signer safes are supported. Multi-signer support should be added for more use-case compatibility. Onchain signatures could be used to avoid the need for backend infrastructure. Offchain signature link sharing could also be used. For example:

• instigator preps tx and sends link with tx info in search params
• each signer opens link, connects wallet, and is prompted to sign the data (with an option to view the tx info on swiss-knife.xyz?)
• after signing, the signer is given another link with the signature data in the search params to pass back to the instigator
• the instigator opens each of the signer links and the signature data is added to local storage
• the original tab is always checking for localstorage updates and will show how many signatures have been collected
• once all signatures are collected, the instigator can sign and execute
• onchain signatures can also be propagated so signers can do either onchain or offchain