* Change History content key to us SSZ Union and adjust tests
* Change slot to byteBE instead of LE
This is currently not specified in the Portal network
specifications, but we are using already BE for the actual content
key, so change it also here to remain consistent.
Currently bootstrap nodes for discv5 and for the Portal nodes
were provided through separate cli arguments. This is however
confusing and cumbersome as typically when (currently) testing
a node will have both discv5 and the Portal networks enabled.
We merge them into one argument.
If a node happens not to support a Portal network, it will be
removed after message request failure.
Commit also contains additional clean-up and nim-eth bump.
* Rename FindNode to FindNodes as per spec
* Use consistently lower case starting camelCase for consts
Style guide nep1 allows for both CamelCase and camelCase for
consts, but we seem to use more often camelCase. Using this now
consistently.
* Change some procs to func
