levels: added swiping tabs to choose between rivers and stations
Reenabled settings fragment

Uses an unofficial support PreferencesFragment
levels: minor filter fixed in RiverSelectionFragment
levels: fixed disappearing fragments when navigating drawer
levels: added pager tabs to data selection fragment
levels: maded RiverSelectionFragment and StationSelectionFragment public
levels: changed tab colors
Cleanup in colors
Minor cleanup in strings
levels: added station count subtitle to GraphActivity
levels: added next item icon to data items
levels: renamed GraphActivity to RiverGraphActivity
levels: removed settings labels from WaterGraph
levels: decouple settings data from setting title in WaterGraph
levels: seekbar starts out with right original position
monitor: MonitorSourceLoader can load all timestamps at once
levels: fixed minor issue with switched labels
levels: simple layout renaming
levels: added very basic level view for single stations

Graph will be added after ODS supports recording sources
levels: selecting river goes to station list