feature: add real vesting module

[liamsi]

Summary

We also want this: agoric-labs/cosmos-sdk#155
We don't want to wait on the SDK to upstream this though.

[rootulp]

Notes from @musalbas

• We may want to add the ability to have custom vesting schedules (e.g. 6 month lock up and then unlock daily after. This scenario requires two separate accounts currently).

[evan-forbes]

during the onsite, we decided to use the standard vesting (lockup) module

[rootulp]

[no change needed] the Cosmos SDK vesting module appears already enabled:

celestia-app/app/app.go

Line 146 in 58352d1

vesting.AppModuleBasic{},

but we may want an additional issue to verify it can be used as expected.