Convert ChartFox interfacing to v2 API.

[mjh65]

This change modifies the ChartFox interfacing to use the latest (v2) API for chart retrieval. The authentication protocols have been updated, so that each Avitab user is required to have a ChartFox login and use their account in order to obtain an authentication token that allows chart retrieval. The new API works similarly to the older API. Some codings have been modified, and georefs are now available (not yet used). Some general and minor refactoring updates are also included in this change, including some renaming of Navigraph-related variables. To enable the new ChartFox interfacing in the build of Avitab it is necessary to define the environment variable CHARTFOX_CLIENTID with the value of a recognised ChartFox client ID before configuring with cmake. The client ID serves to identify Avitab as the requesting application. The user will still be required to authenticate with ChartFox before any charts may be retrieved. This change resolves issues https://github.com/fpw/avitab/issues/149 and https://github.com/fpw/avitab/issues/196.