Implement UniswapV3 positions wrapper

[utgarda]

• [x] claim both rewards in UniswapV3Wrapper per-rata
• [x] put the wrapper implementation in an abstract contract
• [x] bonus points: scout for Reserve hackathon bounties that can make use of the above

[utgarda]

Most of the bounties are about collateral assets with 1 token paid as reward to liquidity providers, 2 at most. 2-token rewards:

• UniswapV3
• Convex(?)
• Aura(?)