Introduce text input field for zoom level and rename input field for GMaps API key to avoid naming collisions

+ Input field for zoom level is required in order to pass zoom level down to field data query method
GMaps view preserves any previously selected zoom level (default is level 16)
Rename text input field for search keywords to 'mykeywords' in order to avoid naming collisions
Extend format of boundary string with a zoom level and take it into account when querying the Niantic API. Default zoom level is now 16.
Take custom zoom level into account when initializing GMaps view
Extend format of boundary string with a zoom level and rename input field for search keywords