EPIC 3.2: Options Dialog and Persistant Settings

[AndreLester]

Expectation: As a GEOSYS subscriber and plugin user, I would like be able to enter my API
credentials once and have them used whenever I use the GEOSYS API.

Acceptance criteria:

1. Given the options dialog is implemented, when a user enters their credentials then those
   credentials shall be persistent across multiple QGIS Sessions.
2. Given the options dialog is implemented, when a user has entered their credentials, then calls to the GEOSYS API shall use those credentials.
3. Given the options dialog is implemented, when selected a geographical region, then any API
   calls will be made to the underlying GEOSYS URL that services that region.
4. Given the paging limit is implemented, when the user performs a search or using the
   processing algorithm, then the number of results will be constrained by the paging limit size.