[mythtv-cmyth] Release v1.8.13

This updates the MythTV PVR addon to v1.8.13.

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Changelog:
 - Fixed crash when reconnecting to the backend                                  
 - Fixed setting bookmarks when using MythTV 0.27 backend                        
 - Fixed usage of priority values (>256)                                         
 - Fixed remaining time zone issues by using UTC based timestamps                
 - Schedule management refactoring                                               
      - Fixed recording rule deletion                                            
      - Fixed handling of backend version specific varieties                     
      - Fixed failed mappings due to gaps in the EPG                             
      - Various smaller improvements and bug fixes                               
 - Provide accurate EDLs for videos with variable frame rate when using MythTV 0.27 backend
 - Added 'Keep Live TV recording' functionality                                  
 - Improved start of Live TV playback