Layer & data: Filter widget for boreholes

[mapcentia]

We need to be able to filter the layers. This means that the user must be able to set a filter for each type of data layer. The filter parameters will differ between the layer types. So the first task is to implement a button for each layer:

The buttons will open a filter dialog. Here how it's done in standard Vidi:

The filter definition must be fixes (the user can't alter it - only set the values), but a system must be implemented, so it's for us to change the definition e.g. add a the parameter. This could be a js module holding the definitions.

The next is to actually apply the filters, but I'll put that in another issue.