Extend cw-vesting to allow for staking in DAOs

[JakeHartnell]

Closes #779

This topic keeps coming up in spaces and I wanted to explore how difficult it would be. This PR is a strawman solution (couldn't help myself 😂). DO NOT MERGE.

Some observations:

• Need to restrict which staking contracts a vesting contract can stake with as that could be a way to sneak out unvested funds if the staking contract is not trusted.
• Not supporting the ability to propose drastically simplifies things as we don't have to worry about deposits getting refunded.
• Not supporting cw20 greatly simplifies things, but we may want to add support for that for use with the $DAO token?
• Doesn't really impact core logic too much and so should be relatively safe and cheep to audit.
• Frontend would certainly require work with this approach... but hard to imagine an approach where that wouldn't be the case.

[NoahSaso]

Features derived from list above and discussion in Monday call:

• Mutable allowlist of contracts the staking contract can interact with (should be instantiated with the voting module / staking contract)
• Ability to passthrough wasm messages to the allowlisted contracts, so that the owner can send returned deposits back to themself for example
• Flag to enable or disable staking (maybe just via the allowlist being empty or not)
• Multiplier for voting power derived from remaining vesting
• Require proposal deposits to be already vested (i.e. liquid and transferrable)

[JakeHartnell]

Related issues we may also want to consider when working on this:

• Enable optional vesting of staking rewards in cw-vesting #710
• Allow cw-vesting to register multiple slashes at once #677

[JakeHartnell]

Limits on voting power for vested tokens could be achieved with #746.

[NoahSaso]

Closing as this is not the design we are going to pursue to add voting support for vesting tokens.