rework hls segmenter (#407)

* rework hls segmenter to start more quickly

* don't use realtime encoding for hls until we're at least a minute ahead

* ugly but functional playlist filtering

ErsatzTV.Core/Interfaces/FFmpeg/IFFmpegSegmenterService.cs

@@ -1,14 +1,11 @@
-using System.Diagnostics;
-using LanguageExt;
+using System.Collections.Concurrent;
 
 namespace ErsatzTV.Core.Interfaces.FFmpeg
 {
     public interface IFFmpegSegmenterService
     {
-        bool ProcessExistsForChannel(string channelNumber);
-        bool TryAdd(string channelNumber, Process process);
+        ConcurrentDictionary<string, IHlsSessionWorker> SessionWorkers { get; }
+
         void TouchChannel(string channelNumber);
-        void CleanUpSessions();
-        Unit KillAll();
     }
 }

ErsatzTV.Core/Interfaces/FFmpeg/IHlsSessionWorker.cs

@@ -0,0 +1,10 @@
+using System;
+
+namespace ErsatzTV.Core.Interfaces.FFmpeg
+{
+    public interface IHlsSessionWorker
+    {
+        DateTimeOffset PlaylistStart { get; }
+        void Touch();
+    }
+}