Cleanup starting and stopping the plugin

Fix storing a pointers to SCCIAdapter objects and properly delete them
when stopping.

Moved creation of the objects required by DVBAPI from DVBAPI::Initialize()
to DVBAPI::Start(). That way it doesn't matter whether the DVBAPI plugin is
loaded before or after the device plugin.

Moved deletion of the objects required by DVBAPI from SCCIAdapter::~SCCIAdapter()
to DVBAPI::Stop(). That way things get cleaned up in the same source area
where they have been allocated.
UDPSocket.cpp: call Cancel(3) in destructor
UDPSocket.cpp: we don't need to associate sCCIAdapter anymore
UDPSocket.cpp: initialize sock variable

The 'sock' variable will be used for handling all camd.socket
communication.
This commit also fixes closing uninitialized variable, which
could close eg. stdout.
Rename UDPSocket to SocketHandler

Currently the file has nothing common with UDP.
Simplify creating and deleting SocketHandler thread.

Also check for Running() in SocketHandler::Action().
SocketHandler: name a thread
Fix SCCIAdapter assigning
Added SCCAMSlot::GetCamName()

In the CAM menu of VDR we get "OSCam" instead of "CAM ready".
Cosmetics: don't add empty lines in "vdr --help"

DVBAPI::CommandLineHelp() shall return NULL (or not be overwritten at all)
if it has nothing to say, as in this case.
Otherwise there are superfluous empty lines in the output of "vdr --help".
LogLevel: fix the input range of the menu item

Added the proper input range (0...3) of the 'Log Level' menu item
in cMenuSetupDVBAPI::cMenuSetupDVBAPI().
Rework cScCamSlot::Process()

Adjust to recent code from vdr-sc
Credits: leslie

Closes #40
Drop CAPMT::get_pmt()

Assume that VDR always provides CA descriptors.