feat(app): Customizable output directories

Added a new Advanced screen, which allows you to choose your own source/destination directory. Also introduces "services" for file management and backups to make maintenance easier down the road.

Author: mrrfv

companion_app/android/app/src/main/AndroidManifest.xml

@@ -3,7 +3,7 @@
     <uses-permission android:name="android.permission.READ_CONTACTS"/>
     <uses-permission android:name="android.permission.WRITE_CONTACTS"/>
     <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
-    <uses-permission android:maxSdkVersion="29" android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
+    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
     <uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />
     <uses-permission android:name="android.permission.READ_SMS" />
     <uses-permission android:name="android.permission.READ_CALL_LOG" />
@@ -34,6 +34,12 @@
                 <category android:name="android.intent.category.LAUNCHER"/>
             </intent-filter>
         </activity>
+        <!-- File picker activity -->
+        <activity
+            android:name="com.flutter.plugin.filepicker.FilePickerActivity"
+            android:exported="true"
+            android:theme="@style/FilePickerTheme" />
+
         <!-- Don't delete the meta-data below.
              This is used by the Flutter tool to generate GeneratedPluginRegistrant.java -->
         <meta-data

companion_app/android/app/src/main/res/values/styles.xml

@@ -15,4 +15,10 @@
     <style name="NormalTheme" parent="@android:style/Theme.Light.NoTitleBar">
         <item name="android:windowBackground">?android:colorBackground</item>
     </style>
+
+    <!-- File picker theme -->
+    <style name="FilePickerTheme" parent="Theme.AppCompat.Light.NoActionBar">
+        <item name="android:windowBackground">@android:color/transparent</item>
+        <item name="android:windowIsTranslucent">true</item>
+    </style>
 </resources>

companion_app/devtools_options.yaml

@@ -0,0 +1,3 @@
+description: This file stores settings for Dart & Flutter DevTools.
+documentation: https://docs.flutter.dev/tools/devtools/extensions#configure-extension-enablement-states
+extensions: