Add ability to define descriptions per Analytic item

[chrispage1]

This PR adds the ability to optionally define a human friendly description for your Analytics.

It taps into the AnalyticRepository and DTO to return the relevant description where it has been defined.

It can be easily set using the existing PanConfiguration helper:

 PanConfiguration::analyticDescriptions([
    'tab-media' => 'Media tab in website header',
    'tab-register' => 'Registration tab on login page'
]);

An example of the output data would be:

[chrispage1]

This is off the back of discussion #29