Add claim module timing variables as module parameters

[sampocs]

Background

Claim module parameters are defined here, but they're not actually stored in the state as true module parameters. A consequence of this is that we cannot easily modify the parameters for unit or integration tests.

Suggested Design

• Rename DefaultVestingInitialPeriod to DefaultInitialPeriodDuration
• Rename DefaultEpochDuration to DefaultSubsequentPeriodDuration
• Store both of those as module parameters:
  • Add them to the params proto
  • Set them in InitGenesis
  • Set them in upgrade handler
• Modify any functions that leverage those values to read them from the store and access them from the params struct
• Change the init_chain.sh script in dockernet to sed & replace the default values with 120 seconds for the DefaultInitialPeriodDuration, and 60 seconds for the DefaultSubsequentPeriodDuration

Acceptance Criteria

• Unit tests and integration tests pass
• Airdrop integration test scripts pass