Make swap fees inclusive

[marco-sundsk]

• Put exchange_fee and referral_fee, as ratios, include in the pool fee.

  Apply this info:

  pub struct InternalFeesRatio {
    /// Portion (bps) of the fee going to exchange in total fee.
    pub exchange_fee: u32,
    /// Portion (bps) of the fee going to referral in total fee.
    pub referral_fee: u32,
  }

  when initial contract, and it can be changed by owner of this contract, normally a DAO, using interface:

  pub fn set_fee_policy(&mut self, fee_policy: InternalFeesRatio);

  In this way, when create pool, the fee param would be the total fee in bps. Exchange_fee and Referral_fee are charge from that total fee according to the bps value assigned in InternalFeesRatio.

• Cause storage changed, a migration is needed.
• provide a new view function to get contract meta info in one shot:

  pub struct Metadata {
    pub version: String,
    pub owner_id: AccountId,
    pub pool_count: U64,
    pub whitelist_count: U64,
    pub fee_policy: InternalFeesRatio,
  }
  pub fn get_metadata(&self) -> Metadata;