Storage List & Storage Map - Get By Index

[TeknoPT]

The ability to get an item by index in both a storage list and storage map.

[Relfos]

Lists already support this.

Maps would benefit from getAllKeys and getAllValues, but that requires new Extcalls in the chain first.

[TeknoPT]

I think adding those 2 methods to the ExtCalls would be ideal, to allow the users to manipulate their storage_maps easier.