Event logger redux

[goolord]

• adds back the event logger as an associated type family. will figure out how to make it easier to case on all of the events later. the best solution is most likely to be maintaining an event product type with the constructors for every event
• adds stake pool initial registration event
• adds stake pool re-registration event
• adds sum of the deposits in a transaction event

previous prs with relevant discussion
#2244
#2356

[nc6]

Looks generally good. A few comments in some areas.