Add Polish keyboard layout to VirtualKeyBoard

Thanks Macnuts
ServiceMP3: Handle sServiceref on getInfoString

eServiceMP3::getInfoString didn't return info for sServiceref.
Without sServiceref Picons for GStreamer services cannot rendered
cause sServiceref was empty.

Signed-off-by: Littlesat <littlesat99@yahoo.com>
display frequency for DVB-C back in Hz

Signed-off-by: Littlesat <littlesat99@yahoo.com>
InfobarGenerics: fix possible GSOD when in movieplayer

Or any other non primer infobar
dvb/db: Refactor static methods

parseFrontendData and similar don't use any class members, so they are
static. No one else needs to know about them, so don't put them into the
public interface (which will also make Python wrappers). Thus make them
static methods so the compiler can do with them as it pleases.
VirtualKeyboard: Remove some whitespaces
dvb/db: Replace "256" with "sizeof", use switch

Avoid magic numbers in snprintf and friends.
Use a switch/case to prevent comparing more then once.
Merge branch 'master' of git://git.code.sf.net/p/openpli/enigma2