feat(google-maps): add missing features and fix wrong definitions (#1815

)

* Update index.ts

* Update index.ts

* Add missing features, and bug fix of methods

* update: classname must be in pascal case

* remove: duplicated class definition

* export encode and spherical static classes

* Add comma

* Fix Encoding and Spherical

* Add convenience methods

* Fix decorators for Encoding and Spherical

* Update: getMap() methods return the instance of the wrapper plugin

* Update: getMap() methods return the instance of the wrapper plugin

* Remove `@CordovaInstance` decorators from getMap()

* Update: GoogleMapOptions (all fields are not optional).

* Follow up:  version `2.0.0-beta2-20170719-2226` of cordova-plugin-googlemaps

* Fix: tslint error

* Fix: tslint error

* No more isAvailable() method.