add actors to movies and shows (#172)

* add actor metadata

* show actors in ui

* get full movie/show metadata from plex

* store actor thumbnail url

* rework movie detail page

* metadata fixes

* rework show detail page

* rework artist page

* code cleanup

ErsatzTV.Core/Metadata/Nfo/TvShowEpisodeNfo.cs

@@ -1,4 +1,5 @@
-using System.Xml.Serialization;
+using System.Collections.Generic;
+using System.Xml.Serialization;
 
 namespace ErsatzTV.Core.Metadata.Nfo
 {
@@ -25,5 +26,8 @@ namespace ErsatzTV.Core.Metadata.Nfo
 
         [XmlElement("plot")]
         public string Plot { get; set; }
+
+        [XmlElement("actor")]
+        public List<ActorNfo> Actors { get; set; }
     }
 }