Standardize usage of ERROR, WARNING, ALERT, INFO in log messages

[ClarkMcGrew]

I believe we have a fairly specific prescription for usage of ERROR, WARNING, ALERT, and INFO in log messages, but it's not applied uniformly.

ERROR -- Things are about to break, should not be ignored

WARNING -- Things users probably don't want to happen, but GUNDAM can continue

ALERT -- Not sure how this is different than warning, just more warning than WARNING?

INFO -- Info about the run (like what file is used) that is important for record keeping and provenance

This is a good place for new people to start contributing. Specific places should be filed as sub-issues.

[riccioc]

If we don't know what the difference is between WARNING and ALERT, should we just use WARNING?

[nadrino]

ALERT is more important than WARNING

[nadrino]

Here is how it was intended for the Logger:

Severity	Color	Context	Implementation
ERROR	Red	Something IS wrong.	Stop runtime and hint the user what should be changed
ALERT	Purple	Something is wrong, but maybe the user is knowing what is doing. (using parameter limit with Eigen decomposition for instance). User should know about it. Purple colour catch the eyes pretty well	Allways printed out
WARNING	Yellow	Important message the user might need to check what's going on during the runtime
INFO	Green	Generic info that indicates the state of the runtime
DEBUG	Blue	Info for devs	Only printed out on DEBUG builds
TRACE	Light Blue	Dev spamming printouts	Never implemented on the main branch

[riccioc]

The definition written by Adrien above can go in the documentation (discussed at the software development meeting).