Activity icon uses now an image instead of a spinner (which was only used as an icon).

Fixed #503.

src/main/res/layout/preference_activity_type.xml

@@ -31,7 +31,7 @@ limitations under the License.
             android:layout_weight="1"
             android:hint="@string/track_edit_activity_type_hint" />
 
-        <Spinner
+        <ImageView
             android:id="@+id/activity_type_preference_spinner"
             android:layout_width="wrap_content"
             android:layout_height="match_parent"

src/main/res/layout/statistics_recording.xml

@@ -68,7 +68,7 @@
             app:layout_constraintRight_toLeftOf="@+id/guideline3"
             app:layout_constraintTop_toTopOf="parent" />
 
-        <Spinner
+        <ImageView
             android:id="@+id/stats_activity_type_icon"
             style="@style/StatsLargeValue"
             android:layout_width="wrap_content"

src/main/res/layout/track_edit.xml

@@ -63,7 +63,7 @@ limitations under the License.
                         android:selectAllOnFocus="true" />
                 </com.google.android.material.textfield.TextInputLayout>
 
-                <Spinner
+                <ImageView
                     android:id="@+id/track_edit_activity_type_icon"
                     android:layout_width="wrap_content"
                     android:layout_height="match_parent"