[pvr.tvh] add missing lock
[pvr.tvh] remove the m_startCond, I don't think it's needed
[pvr.tvh] add missing htsmsg_destroy calls
[pvr.tvh] use the same values when logging subscribe/unsubscribe
[pvr.tvh] introduce a class representing a subscription
[pvr.tvh] update the subscription management to operate on a member of 
type SSubscription instead of four different member variables. This commit 
also fixes a bug where a subscription would be restarted on reconnect if the 
unsubscribe message could not be properly sent to the backend.
[pvr.tvh] change return value of SendSubscribe to void since it's not used 
anymore
[pvr.tvh] use the same formatting in SendSubscribe as in SendUnsubscribe
[pvr.tvh] handle subscription errors correctly (error is a string, not an integer) 
and actually log the precise error reason
[pvr.tvh] bump subscribe/unsubscribe error log severity to error
[pvr.tvh] fix typo in log messages
[pvr.tvh] make the whole thing actually work

I haven't really used static variables in C++ before so I didn't really know how 
they work and behave
[pvr.tvh] fix bug in addon creation that led to startup failures
[pvr.tvh] don't return all groups when XBMC asks for radio groups

This causes XBMC to remove all TV groups and startup only to recreate them 
a second later when it actually wants to fetch TV groups
[pvr.tvh] reduce variable scope
[pvr.tvh] properly initialize STimeshiftStatus in its constructor
[pvr.tvh] prefer prefix ++/-- operators for non-primitive types
[pvr.tvh] remove unused variables
[pvr.tvh] plug potential memory leak
[pvr.tvh] fix dangerous iterator usage