[feature] Impermanent Loss Protection

Fixes #794 (closed)

This change adds impermanent loss protection. When a liquidity provider experiences impermanent loss when withdrawing, a certain percentage of that loss is recovered, by sending rune from the reserve (block rewards bank) to the pool and rewarding the pool units to the withdrawer. This percentage is calculated by measure how long they have been a liquidity provider since the last time they deposited. By default, 100 days is required to get 100% protection, but this can be controlled via an Mimir setting. Mimir also has the ability to set this number to zero, which disables impermanent loss protection.