* locktower components and tests
* integrate locktower into replay stage
* track locktower duration
* make sure threshold is checked after simulating the vote
* check vote lockouts using the VoteState program
* duplicate vote test
* epoch stakes
* disable impossible to verify tests
* Rename userdata to data
Instead of saying "userdata", which is ambiguous and imprecise,
say "instruction data" or "account data".
Also, add `ProgramError::InvalidInstructionData`
Fixes#2761