Importing metadata without signature

[prybalko]

as an interim solution, we should remove a number of web2-style restrictions (presumably intended as safeguards, but ultimately centralising and authoritarian-friendly):

• possibility of importing metadata without signature, e.g. from polkadot.js - whenever this info is used for signing, it should be noted discretely to the user that the data is unsigned.

[camfairchild]

I think a better solution is allow adding multiple signers for a single chain. This would allow using whichever metadata portal is updated first.
Currently you must remove the network, and I believe reset the app to change signers.