[cppmyth] MSVC doesn't initialize int to zero

Override default constructor to initialize int types to zero.
[mythtv] Improves loading of resources

Build channel containers in one pass.
Loadings are handled by event thread on status CONNECTED. By the way
now channels update is triggered too on wake.

Conflicts:
	addons/pvr.mythtv/src/pvrclient-mythtv.cpp
[cppmyth] cmake: fix install destinations
[mythtv] fix external includes
[cppmyth] fix virtual members where required