Add Version to ConsensusParams

[ebuchman]

Follow up to #2468, this is the final piece of ADR-016, to allow apps to update their version without a restart.

Originally ADR-016 proposed adding a new field to EndBlock for updating versions, but it was realized in #2636 (comment) that it might make more sense to just add it directly to the ConsensusParams.

Note we forgot to update the changelog in ADR-016 when it was updated for this change in #2667

[ebuchman]

#3152 makes this non protocol breaking. Bumping it back

[b00f]

I have an idea. Out of box idea, Instead of changing protocol. What we need is an external application, lets call it AppSelector.
Changing protocol to support possible fork or updates will make codebase nasty. This messy code currently is applied Ethereum. Look here

AppSelector will run the application but it can manage versioning. AppSelector:

• Monitor the blockchain. Anytime the AppVersion changes it will automatically find the new version (possibly from GitHub release page) and run the required verision
• It can be programmed to start new version at a certain height.