Log levels

from https://github.com/status-im/nim-beacon-chain/issues/205

• NOT noteworthy events that are unusual as far as normal operation goes: (deep?) chain reorgs, slashings etc
• INF logs anything that is sufficient to recreate the state along important checkpoints in the application, but does so in a minimal way, so as not to overwhelm log collectors - minimal in this sense means that it strives to avoid duplicating the same information - kind of like a normalized database - people running the app on a server should not be discouraged from always keeping INF on
• DBG denormalizes the above and adds more checkpoints - repetition for convenience is ok, but we still keep it out of tight loops - developers will have this on by default
• TRC anything goes