Remove MsgAddShares message

[lumtis]

MsgAddShares message allows a coordinator to directly allocate shares for an account in a campaign

This message is a way to automatically perform the following operations:

• Mint vouchers
• Redeem the vouchers for a specific account

With special allocation, we now have a specialized framework to define genesis distribution for accounts decided by the coordinator. This solution is more flexible for the coordinator since the genesis distribution can be changed at any time before the launch of the mainnet. While adding shares is a non-reversible operation, the coordinator can't remove the share from the account (since it is similar to redeeming vouchers which is censorship resistant)

I suggest removing MsgAddShares message from the campaign module. The coordinator should rely on special allocation for genesis distribution
For adding shares to an account directly, the coordinator can perform the two actions:

• Mint vouchers
• Redeem the vouchers for a specific account

Sending those two messages is an operation that can be abstracted from the front-end, client communicating with SPN
The other benefit of removing the message is that we would have a single-entry point for allocating shares in a campaign, minting vouchers. This simplifies state transitions of the module and make it more maintainable

[lumtis]

As discussed, let's work on it