wallet: configuration should be created if it does not exist

[autholykos]

Describe what you want implemented
During the first run of the wallet, if the configuration .toml does not exist, it should be generated on behalf of the user and placed in the default folder.
Describe "Why" this is needed
A user should be able to change configuration parameters.

Describe alternatives you've considered
The generation could be interactive (e.g. through a wizard process) or it can be as simple as telling the user where the configuration gets created (so she can twick it by herself).

[t00ts]

As per yesterday's conversation, the wallet was going to be shipped with a valid configuration file pointing to a running cluster. That was the sole reason as to why this (rather large) refactor was done.

Is this no longer the case?

cc @Fulviuus