Use MIME types in OPML import intent filter

File extensions are widely unreliable - extraneous dots in a file's path will break intent filters
relying on pathPattern's wildcard character, and some applications will omit file extensions
altogether when sending intents (e.g. K-9 Mail). Using MIME types will occasionally catch non-OPML
files in the filter, but it is currently the best option available.

Fixes #1758

app/src/main/AndroidManifest.xml

@@ -175,16 +175,15 @@
                 <category android:name="android.intent.category.DEFAULT"/>
                 <category android:name="android.intent.category.BROWSABLE"/>
 
-                <data
-                    android:host="*"
-                    android:pathPattern=".*\\.opml"
-                    android:scheme="file"
-                    android:mimeType="*/*"/>
-                <data
-                    android:host="*"
-                    android:pathPattern=".*\\.opml"
-                    android:scheme="content"
-                    android:mimeType="*/*"/>
+                <data android:mimeType="text/xml"/>
+                <data android:mimeType="text/x-opml"/>
+                <data android:mimeType="application/xml"/>
+                <data android:mimeType="application/octet-stream"/>
+
+                <data android:scheme="file"/>
+                <data android:scheme="content"/>
+
+                <data android:host="*"/>
             </intent-filter>
         </activity>
         <activity