mobile: iOS naming and API fixes for generators and Swift (#3408)

* build: modify the iOS namespace to iGeth (gomobile limitation)
* mobile: assign names to return types for ObjC wrapper
* mobile: use more expanded names for iOS/Swift API

mobile/primitives.go

@@ -32,7 +32,7 @@ func (s *Strings) Size() int {
 }
 
 // Get returns the string at the given index from the slice.
-func (s *Strings) Get(index int) (string, error) {
+func (s *Strings) Get(index int) (str string, _ error) {
 	if index < 0 || index >= len(s.strs) {
 		return "", errors.New("index out of bounds")
 	}