SlingboxLib: Fix alternative CSlingbox constructor

CSlingbox::CSlingbox(const char * szAddress, unsigned int uiPort /* = 5001 */) {
  // Call default constructor
  CSlingbox();
  ...
}

"CSlingbox();" - object is created and immediately removed.
Therefore with CSlingbox(const char * szAddress, unsigned int uiPort /* = 5001 */) class members will not be initialized.
[pvr] fix unnecessary creation of new CPVRChannel instances
[AE] Rename ActiveAEResample to ActiveAEResampleFFMPEG
[AE] Move utility functions to AEUtil
[AE] Add factory for AEResampler
[rbp] Hardware accelerated resampling

This replaces the format conversion, up/down mixing and resampling code from ActiveAE with a GPU accelerated version.
Should significantly reduce CPU when using paplayer or dvdplayer.

Requires updated firmware
[resamplepi] Add GPU accelerated option to resampling options
[darwin] - sync xcode project
[win32] - sync project
[PVR] bump add-ons
[visualizations] properly deinit presets dialog in order to avoid focus and scrollposition changes (fixes #15478)
[keyboard layouts] use English language names

Also added small comment to guide future contributors.
[configure] libflac is not a hard dependency now
[linux] - update docs/README.*
Merge pull request #5519 from FernetMenta/pvr

[PVR] bump add-ons
[vfs] Fix asserts when CWin32File is used for drive
Merge pull request #5523 from mkortstiege/vis_presets_list

properly deinit visualisation presets dialog (fixes #15478)
[vfs] Win32Directory: fix Exists() for root folders
Merge pull request #5525 from uNiversaI/keyboard

[keyboard layouts] use English language names
Merge pull request #5479 from popcornmix/resample_factory

[AE] Add resample factory and Pi accelerated resampling