Reconsider warnings about std libs

[andrius-puksta-sensmetry]

Points to consider/rework about the warnings:

• annoying
• unnecessarily scary (they're informational, so should not be warnings)
• imprecise: in many cases where they're printed they don't actually affect the behaviour/output of the command

Therefore, should consider:

• removing them in favor of command-specific information (e.g. print "standard library usages are ignored" in sysand info usages)
• describing in docs why std libs are ignored
• not ignoring std libs for `sysand add - arguably it's better to allow std libs by default