rpcserver/exchanges: Add additional param checks plus other minor bugfixes/improvements (#652)

* deleting the unwanted file created during testing + adding more verbose errors for cli

* wip

* checking params throughout wip

* improving errors

* wip

* thrasher patch

* better err name

* whip

* testing and fixing errors WIP

* upgrades and better errors

* broken test

* wip

* adding some tests

* using tempDir

* mini improvement

* little changes

* better time check

* fixing error

* more glorious changes

* end of day wip

* shazzy changes

* checking error

* appveyor

* last changes:

currency/manager.go

@@ -159,7 +159,7 @@ func (p *PairsManager) IsAssetEnabled(a asset.Item) error {
 	}
 
 	if !*c.AssetEnabled {
-		return errors.New("asset not enabled")
+		return fmt.Errorf("asset %s not enabled", a)
 	}
 	return nil
 }