Use std::sort with comparator for meta dex objects
Copy add_mdex_fields content to MetaDexObjectsToJSON
Split sorting of meta dex objects and adding data

Also removed tx hash check in MetaDexObjectToJSON, as it's no longer required.
Remove add_mdex_fields
Merge pull request #201 from dexX7/mcore-sort-offers

Sort trade offers and replace add_mdex_fields