Update vaults to use sdk.Dec shares

[drklee3]

• Fixes share issuing for deposits after share value increases.
• User can withdraw with sdk.Coin amount and receive the requested amount.
• In some cases account value may be 1 coin less than deposited. Deposit 100, but account value is would be 99. This should be at max 1 ucoin, e.g. 1ukava or 0.000001 kava.