levels: basic activity layout
ods: added missing close cursor in OdsContentProvider
Cleanup LoaderCallback classes
levels: added simple list view for river list
levels: display station count next to water name
lib: aded graphview
levels: added basic levels graph
levels: added background for graphs
levels: filter stations that are not measuring water levels
levels: futher data cleaning.

Some measuring stations just offer relative data without any relations
to get an absolute value. Current tactic is to skip those measurements.