Adopt meta DEx reserved balances on RPC layer

With PR #223 all regtests pass, for the first time! ;)
```
Test summary:

ExodusPurchaseTest ... successful
PropertyCreationTest ... successful
P2SHTest ... successful
MetaDexPlanTest ... successful
MetaDexCancelAtPriceTest ... successful
MetaDexCancelPairAndLookupTest ... successful
MetaDexCancelEverythingInSameEcosystemTest ... successful
MetaDexCancelEverythingIgnorePropertyTest ... successful
MetaDexCancelEverythingScopeTest ... successful
DexCrossEcosystemSideEffectsTest ... successful
TraditionalDexTest ... successful

11 of 11 tests successful
```

https://gist.githubusercontent.com/dexX7/061c73f7d4eec0a2e767/raw/
Strictly: `AVAILABLE` = `BALANCE` + `PENDING` where `PENDING` is actually negative.

A comment like "BALANCE + PENDING" would imply it reports unconfirmed, incoming amounts, not subtracting outgoing ones. Hm..