Move to weacast-leaflet or make it less specific

[claustres]

This module contains mixins and others things that are vue-specific and should be directly integrated into the demo application template. Similarly we are tightly coupled to some leaflet plugins that might not be relevant for others applications: https://github.com/socib/Leaflet.TimeDimension and https://github.com/mikeskaug/Leaflet.Legend.

We should focus here on providing a thin layer to easily integrate the Weacast API in others application and mapping libraries like Leaflet.

[claustres]

Initiated https://github.com/weacast/weacast-leaflet, which will replace this module for forecast layers. Moved the client API layer to be part of the core module: https://github.com/weacast/weacast-core/tree/master/src/client. This module will not evolve anymore and will only be maintained as long as required to support the demo application.