With this commit we extract the wallet creation/unlocking and
initialization completely out of the main function. This will allow us
to use custom implementations in the future.
We move some of the wallet related functions into the new file that
houses the new customizable implementations for some of our interfaces.
Since the next customizable interface will be the wallet, we move those
wallet and chain backend related helper functions.
NOTE: This is a pure code move.
As a preparation for making more and more implementation details
configurable, we add a new ImplementationCfg struct that houses all the
interfaces that can be defined externally.
