[1][Exchange] Allow Fee for orders to be changed correctly

1) MarketFee displays incorrect
Should be `1%` from `Total`, but it is still `0` instead of `100`.

Also this field is editable. Should be disabled.

2) No ability to select "Fee" instead of BTS (do not pay attention to this screenshot because it is from testnet). We should list any user asset if:
- This asset has enough funds in Fee Pool (in BTS) (Asset X Fee Pool > CREATE_ORDER_FEE)
- User has enough funds of this asset to pay Fee (Asset X CER * Fee costs >= User balance of Asset X)

No files or tests are named. Start at the Exchange order fee controls and trace the market-fee display and fee-asset selection described here. Done means the displayed fee is correct, the market-fee field is disabled, and eligible user assets appear only when the stated fee-pool and balance conditions hold.

Written by the indexing model from the issue text.