Add user-defined button labels with color change on press

- PrefsHelper: PREF_LABEL1, PREF_LABEL2 constants
- SettingsActivity: EditText fields with Done-keyboard action to save labels
- MainActivity: buttons show user label, colorAccent on press, textAllCaps disabled
- activity_main.xml: textAllCaps=false for case-sensitive labels

android/app/src/main/res/layout/activity_main.xml

@@ -26,6 +26,7 @@
             android:layout_height="200dp"
             android:text="1"
             android:textSize="24sp"
+            android:textAllCaps="false"
             android:enabled="false" />
 
         <Button
@@ -35,6 +36,7 @@
             android:layout_marginStart="16dp"
             android:text="2"
             android:textSize="24sp"
+            android:textAllCaps="false"
             android:enabled="false" />
 
     </LinearLayout>

android/app/src/main/res/layout/activity_settings.xml

@@ -45,6 +45,49 @@
         android:layout_marginTop="24dp"
         android:layout_marginBottom="16dp" />
 
+    <TextView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:text="@string/section_labels"
+        android:textSize="14sp"
+        android:textStyle="bold"
+        android:layout_marginBottom="8dp" />
+
+    <LinearLayout
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:orientation="horizontal"
+        android:layout_marginBottom="16dp">
+
+        <EditText
+            android:id="@+id/labelRelay1"
+            android:layout_width="0dp"
+            android:layout_height="wrap_content"
+            android:layout_weight="1"
+            android:hint="@string/hint_label_relay1"
+            android:maxLines="1"
+            android:inputType="text"
+            android:imeOptions="actionDone"
+            android:gravity="center" />
+
+        <EditText
+            android:id="@+id/labelRelay2"
+            android:layout_width="0dp"
+            android:layout_height="wrap_content"
+            android:layout_weight="1"
+            android:hint="@string/hint_label_relay2"
+            android:maxLines="1"
+            android:inputType="text"
+            android:imeOptions="actionDone"
+            android:gravity="center" />
+    </LinearLayout>
+
+    <View
+        android:layout_width="match_parent"
+        android:layout_height="1dp"
+        android:background="?android:attr/listDivider"
+        android:layout_marginBottom="16dp" />
+
     <TextView
         android:layout_width="match_parent"
         android:layout_height="wrap_content"

android/app/src/main/res/values/strings.xml

@@ -55,6 +55,11 @@
     <string name="button_close">Sluiten</string>
     <string name="button_cancel">Annuleren</string>
 
+    <!-- Label customization -->
+    <string name="section_labels">Knoptekst</string>
+    <string name="hint_label_relay1">Relay 1</string>
+    <string name="hint_label_relay2">Relay 2</string>
+
     <!-- Theme -->
     <string name="section_theme">Weergave</string>
     <string name="theme_system">Systeem</string>