Feature/january changes 3 (#226)
* Added placeholder until play example
* Added playback stalled feature in iOS
* Added playback stalled feature in iOS
* BetterPlayerTheme addition, custom controls rework
* Exposed BetterPlayerPlaylistState and betterPlayerController getter within.
* Overridden duration implementation
* Overridden duration implementation
* Overridden duration implementation
* Overridden duration implementation
* Updated readme, general refactor
* PR refactor
* iOS PiP implementation
* iOS PiP implementation
* PiP Android implementation
* PiP Android implementation
* PiP Android implementation
* PiP Android implementation
* Fixed notification service
* PiP documentation update
* PiP implementation update
* PiP implementation update
* PiP implementation update
* PiP implementation update
* iOS PiP implementation
* iOS PiP implementation
* Lint fixes
* Format fixes
* Merge fix
* Removed skipsTimeInMilliseconds. Added forwardSkipTimeInMilliseconds and backwardSkipTimeInMilliseconds.
* Fixed event play/pause event not triggered when controlling video with PiP or remote notification.
* General refactor
* Fixed progress bar able to drag over other buttons
* Lint fixes / dartfmt
* Lint fixes / dartfmt
* Better Player 0.0.45
* Lint fix
