Slashing/jailing naming refactors are needed

[shaspitz]

Problem

Last minute changes like https://github.com/cosmos/interchain-security/pull/692 have made a lot of the semantics around slashing/jailing outdated. We should revisit these naming semantics once the future plans for slashing, untrusted consumers, etc. are more ironed out.

Closing criteria

Naming semantics around slashing/jailing are properly refactored.

Problem details

• HandleSlashPacket now only handles downtime packets, and mainly just jails a validator. It could be renamed to HandleDowntimeSlashPacket, JailFromDowntimePacket, etc.. something that can now be more descriptive
• SlashMeter is really a "jail meter". We're limiting validator jailings over time, not slashing
• SlashPackets are no longer used to enforce slashing, they're used to either log, or jail. InfractionPacket could be appropriate here
• These are just examples, there might be more refactors needed