Update mechanism to connect to the node

[Warchant]

Currently if a user does not have a connection to a parachain node (GGX node) it does not print any errors.

Refactor this to make sure user can select a node (enter URL or select pre-hardcoded, like in polkadot.js).

See #56
Main code that connects to a node and creates Context is done, the task is to fix all tests.