[Media upload] Media pre-processing (#403)

* Create `mediaupload` module for media pre-processing.

* Split `mediapicker` and `mediaupload` modules.

libraries/core/src/main/kotlin/io/element/android/libraries/core/mimetype/MimeTypes.kt

@@ -31,6 +31,10 @@ object MimeTypes {
     const val Jpeg = "image/jpeg"
     const val Gif = "image/gif"
 
+    const val Videos = "video/*"
+
+    const val Audio = "audio/*"
+
     const val Ogg = "audio/ogg"
 
     const val PlainText = "text/plain"