Improve user facing messages

[janos]

Most of swarm messages that are logged are developer centric and cryptic to a user. They are not written with user experience in mind.

Separate exposed information in different log levels in a way:

• Info and more severe log levels (Warn, Error) should not expose internal implementation details or to reveal as less as possible, but be focused on used and clarity of actions required to the usage of swarm
• Trace and less severe log levels may expose implementation details

Keep log messages as shot as possible. For example, it is not needed to state that the problem/error has happened if Error log level is used.

Investigate if Trace logs can be logged separately (stored on disk) for debugging purposes if log level is set to Info or higher severity. Investigate if stack traces can be preserved on disk in case of panics for crush reporting by users instead printing stack traces to standard output.