feat(store): improve errors

[polydez]

In this PR we improve error statuses returned by the some store API.

Initially it was needed by #504 (I wanted to be able to process "account not in DB" errors), but finally it became unused due to changed solution. But it might make our API better, so I propose to keep these changes.

[Mirko-von-Leipzig]

I think this is good improvement.

There are still possibilities where the mapping might be the wrong default for some situations; e.g. if we have bad internal state and attempt to retrieve an unknown block then that shouldn't be exposed.

Though I think this will always remain the case; and this PR at least restrains the default non-internal mappings to a smaller set.

[polydez]

There are still possibilities where the mapping might be the wrong default for some situations; e.g. if we have bad internal state and attempt to retrieve an unknown block then that shouldn't be exposed.

Yes, for such cases we can map it to whatever we need. :)

[bobbinth]

Looks good! Thank you!