Add possibility to pass list of node peers when constructing CasperClient in casper-js-sdk

[devendran-m]

After 1.5 not all nodes will sync to Genesis. So it’s possible to call chain_get_block on a node that doesn’t have this certain block. Currently, the SDK will throw Returned block does not have a matching hash. which is good. But to make it more convenient, we can give the user possibility to provide a list of peers, and SDK will then try every provided node in order before throwing mentioned message.

[RitaMAllenCA]

@hoffmannjan can Ryo do this?

[hoffmannjan]

this is something that will be required past 1.5 so yes - but I would treat it as lower priority