Qt4 - Try to fix the detection of video tracks and show of related buttons, fix a segfault that can happen.

Missing some cases that I could not test.
Also ffmpeg/chroma.c is locked, so I can but leave it broken.
Fix is for the remaining modules is obvious and the issue is easy to detect.

better now, thanks for j-b for spotting.

maininputmanager which listens p_intf->p_libvlc "volume-change" variable
for volumechange. ref #1365

biggest polls in qt4-interface, still maybe few to go. ref 1365

it.

Patch by Rémi Duraffort.

Qt4 - MainInterface cleaning, FIXME labelling, Simplification, put the delay of status Toolip to 3s, re-ask the privacy dialog if closed the previous time without a correct validation before.
Commit from NYC/NY/Columbia University ;)

Fix play/pause toggle
Removes 2 unused signals

Enforce access to input_item_t through input_item_{G,S}et*()
Unlock mutexes before calling these functions
Free strings returned by input_item_Get*()

New functions added:

char * input_item_GetURI( input_item_t  * )
void input_item_SetURI( input_item_t * , char * )

mtime_t input_item_GetDuration( input_item_t * )
void input_item_SetDuration( input_item_t * , mtime_t )

to access input_item_t->psz_uri and input_item_t->i_duration