See https://github.com/EFForg/rayhunter/issues/334
Severity levels low, medium, high are now exposed to the UI in form of
dotted, dashed and solid lines. The line on the UI represents the
highest-so-far severity seen.
Originally this was intended to be represented by Yellow/Orange/Red, but
this would mean yet another divergence for colorblind mode. This is
colorblind-friendly by default (I think...)
As part of this, simplify EventType so that it becomes a flat "level"
enum without nested variants.
There is also a new debug endpoint that allows one to overwrite the
display level directly for testing.
