Simplify MimeType class and parse mimetypes in a more lenient way

modules/store/src/main/scala/docspell/store/syntax/MimeTypes.scala

@@ -12,11 +12,16 @@ object MimeTypes {
 
   implicit final class EmilMimeTypeOps(emt: emil.MimeType) {
     def toLocal: MimeType =
-      MimeType(emt.primary, emt.sub, emt.params)
+      MimeType(emt.primary, emt.sub, None)
+        .withCharsetName(emt.params.get("charset").getOrElse("unknown"))
   }
 
   implicit final class DocspellMimeTypeOps(mt: MimeType) {
     def toEmil: emil.MimeType =
-      emil.MimeType(mt.primary, mt.sub, mt.params)
+      emil.MimeType(
+        mt.primary,
+        mt.sub,
+        mt.charset.map(cs => Map("charset" -> cs.name())).getOrElse(Map.empty)
+      )
   }
 }