Tracking: add macro HAVE_SKYLINES_TRACKING

Prepare for allowing SkyLines tracking without HTTP client.
Tracking: add macro HAVE_LIVETRACK24

To replace HAVE_TRACKING where only LiveTrack24.com support is being
checked.
SkyLines/Tracking: don't use HAVE_TRACKING

In Tracking/SkyLines/Features.hpp, decide whether tracking is
available without consulting HAVE_TRACKING.  HAVE_TRACKING will not be
enabled by HAVE_SKYLINES_TRACKING, not the other way round.
OS/SocketDescriptor: enable sendto()/recvfrom() on Windows CE
OS/SocketAddress: convert Port() to a static method
OS/SocketAddress: assign INADDR_ANY in MakePort4()
OS/SocketAddress: build on Windows CE

Disable the Lookup() method because getaddrinfo() is not available.
OS/SocketDescriptor: use SocketAddress::MakePort4()
OS/SocketAddress: add static method MakeIPv4Port()
Tracking/SkyLines: pass SocketAddress to Open()

Use SocketAddress::MakeIPv4Port() instead of SocketAddress::Lookup().
The former doesn't require getaddrinfo().
Tracking/SkyLines: enable on Windows CE

Our code base is finally ready to support UDP networking on Windows
CE.  Unidirectional currently, due to lack of IOThread.
Util/RadixTree: apply naming convention
Waypoints: normalise the string for SuggestNamePrefix()

Allows using lower-case letters on the hardware keyboard.
DataField/Boolean: inline GetAsBoolean()
VegaDemoDialog: use DataFieldBoolean::GetAsBoolean()
dlgWeather: convert runtime checks to assertions
DataFieldEnum: add method GetValue()

Less overhead than GetAsInteger(), because it's not virtual.
DataField/Enum: make the Set() argument unsigned

It's all unsigned internally.
InfoBoxes/.../Factory.cpp: Harmonized Captions for Atlitude, Height and Elevation.
Panels/GlideComputerConfigPanel.cpp. Caption change L/D to GR.