refactor: refactor x/exchange module

[kingcre]

Description

• Use sdk.Int for quantities
• Simplify fee calculation and ceiling/truncation for order amounts
• Move min_order_quantity, min_order_quote from x/amm Pool into x/exchange Market and also add max_order_quantity, max_order_quote
• Move fees and quote coin dust into Market's fee_collector
• Change MaxPrice to 10^24
• Store price as tick indexes

[richard-bachman]

Thank you for drafting this PR.
After reviewing the overall codebase, the followings are the highlights.

• Add test suites and simulations for order source orders and their matching
  • This test for order source orders is very important since this is the part to interaction with other module for order like amm.
• Can we check the matched price and matched amount in Batch_test?
  • Currently, only last price is checked.
• Much more comments above the functions/variables to explain what they are (even though the explanation is short and brief.
• Please remove all // TODO: ... part.
  • Others cannot know if it is not completed parts or to be completed or to be discussed further.
  • Please make the discussion in order to resolve all TODO: part ASAP.
• What if the max value of life span of limit order?
• Please complete spec.
  • Need to explain in detail about mid-block processing since this is the new concept.
  • Events, README need to be completed

Other detailed comments are added as inline comments.

[richard-bachman]

@kingcre In L47 of exchange/keeper/batch.go, we have the following now.

if !matched {
	return
}

But, due to the code in L20 as follow,

if bestBuyPrice.LT(bestSellPrice) {
	return nil
}

we might not have the case of !matched. Is this for sanity check? Or, is there other case of not matching?

[kingcre]

@kingcre In L47 of exchange/keeper/batch.go, we have the following now.

if !matched {
	return
}

But, due to the code in L20 as follow,

if bestBuyPrice.LT(bestSellPrice) {
	return nil
}

we might not have the case of !matched. Is this for sanity check? Or, is there other case of not matching?

Yes, as you said matched should always be true. It'd be better to transform it into a sanity check. Thanks.

[kingcre]

Closing. See #223