Custom defined KPI targets

[ecumike]

Currently, from the original implementation, there are hardcoded 'realistic' KPI targets in the dashboard view reports_dashboard:

        'fcp': {
            'fast': 1.6,
            'slow': 2.4
        },
        'fmp': {
            'fast': 2,
            'slow': 3
        },
        'tti': {
            'fast': 3,
            'slow': 4.5
        },

These drive the 3 pie charts on the dashboard as to what %s of URLs are in each of these ("average" is the # range between "fast" and "slow").

Ideally these should be a model to allow each implementation to set their own targets, as well, it will allow these to easily be changed without having to redeploy your app.