Add a process to configure the initial set of resources in case showing everything is too much

[Aklakan]

After or maybe even during configuration of the sparql connection the faceted search components should not be configured with the actual data providers right away.
Instead, a panel that allows inspecting the amount of data and configuring a base concept should be shown first.

In general, this panel should provide a button that performs a probing query for whether the currently selected amount of resources can be processed

For specification of the initial set of resources this panel could for example allow for

• just selecting all subjects
• selecting among the sets of instances for given set of classes (i.e. the values of the type facet without counts)
• the option to select subjects or objects of one or properties