Terrain: check validity of terrain color ramp array size
Profile/TerrainConfig: Ignore invalid/unsupported color ramp setting
Terrain/TerrainRenderer: Add white terrain color ramp

Implements trac enhancement request #2581.

The white ramp is only useful if terrain shading is disabled.
Dialogs/Traffic: make attributes const
Dialogs/TrafficList: auto-disable the "Details" button
Dialogs/TrafficList: use Layout::GetTextPadding()
OpenGL: Replaced NULL by nullptr
This fixes a build failure on the Raspberry PI
Merge branch 'master' of git://github.com/steffenpassmann/XCSoar
Dialog/TrafficList: eliminate duplicates
Dialogs/TrafficList: show position if available
Volkslogger: change flightdownload path to TCHAR

Make compiling possible with UNICODE
Volkslogger. Implement VL Flightlog index in RecordedFlightInfo

Add Volkslogger internal index of downloaded
flight log to struct RecordedFlightInfo.
Volkslogger: vlconv reenable mktime()

mktime was commented out however it is necessary for
the routine to work.
It normalizes the broken time format after parsing
binary data and after summations/subtractions.
DeviceListDialog: fix reversed GetState()==READY check

Fixes flight download (regression by d327428c).
DeviceListDialog: show error message when port is not ready
Android/BluetoothHelper: add function isEnabled()
DeviceListDialog: show "Bluetooth disabled" error message
Manual: Separated some none i10n items from tex files.