BDIP19 (Formal vote): Incentivize long-term LP stakers

This is similar to the current proposal under consideration by https://mith.cash/ This is also similar to Ampleforth's Geyser and Radix's Multiplier model.

At present, people can add & remove liquidity to LP farms with no cost, and people can add & remove liquidity to Seignorage stake with the cost of a lock-up period of 4 epochs (2 days).

I do not believe such rewards should accrue to Seignorage stakers as they bear no impermanent loss risk.

Therefore, I propose long-term incentives for LP stakers in the form of an up to 3.0x rewards multiplier that rises linearly depending on how long they stake.

Proposal: 3.0x linear multiplier for up to 6 months staking on LP farms (not Seignorage staking).

Advantages:

1. Incentivizes long-term participation in providing liquidity to the platform.
2. If BDIP18 passes, long-term LP & Seignorage stakers' benefit from the multiplier effect will help offset any negative illiquidity implications of the rewards vesting.