[mythtv-cmyth] Add an abstract class MythFile::StreamHandler

BasicStreamHandler is the default implementation for StreamHandler. It provides basic Read, Seek, Position and Length from old class MythFile. MythFile::StreamHandler or BasicStreamHandler can be extended to provide most advanced services. The method  MythFile::RegisterStreamHandler() allows to plug a new stream handler.
[mythtv-cmyth] Add new implementation for MythFile::StreamHandler

New class EdlStreamHandler implements  MythFile::StreamHandler and provides internal EDL functionalities.
[mythtv-cmyth] Enabling Internal EDL

When internal EDL is activated then configure and plug EdlStreamHandler to the playback.

- Add setting g_iEdlMethodType  to choose the method (PVR | Internal)
- Add global g_bEdlEnbaled to switch On/Off EDL functionality with menu hook
- Add Menu hook menuHookSwitchOnOffEdl
- Add notifications about EDL status