Create Node class to lay groundwork for better node handling.

[cyon1c]

Nodes should hold a little more information outside of uri - ie, status, prefix, version, etc. (Dynamic Global Properties + some extra stuff). This will allow us to start building a more intelligent node handling framework within steem-python.

This is part of the attempt to remove the SQL Config from steem-python. Reference issue #216 .

[bobinson]

When you say "more intelligent node handling" does that also means handling scenario which are down / unrechable ?

[cyon1c]

We haven't devised a spec yet for this, but that is certainly part of the intended enhancements.