Make LenaPi usable on Android devices

- Add app icon
- prevend android device from shutting down cpu while playing music
- fix scaling bug
- fix energy saver for RasPi by reconnecting to music player
- minor refactorings and renaming

LenaPi/controllers/StyleHandling.h

@@ -0,0 +1,81 @@
+#ifndef STYLEHANDLING_H
+#define STYLEHANDLING_H
+
+#include <QObject>
+#include <QQmlContext>
+#include <QQmlPropertyMap>
+
+/**
+ * @brief Contains all style sizes, margins and paddings used throughout the application
+ *
+ * Based on a reference screen size, maps for scaled margins, paddings and spacings are created and
+ * registered in the QML context. The values stored in the maps can then be used from QML.
+ * Map names: StyleSizes, StylePaddings, StyleSpacings, StyleMargins
+ *
+ * Always use values from these maps in QML! Never use magic numbers! They will NOT scale when
+ * the application is run on a different screen.
+ *
+ * See https://doc.qt.io/qt-5/scalability.html
+ *
+ * @todo scale fonts as well?
+ * @todo use dpi for scaling as app is very small on Android?
+ */
+class StyleHandling : public QObject
+{
+    Q_OBJECT
+public:
+    explicit StyleHandling(QObject *parent = nullptr);
+
+    /**
+     * @brief Calculates ratio, initializes all maps and registers them in QML context
+     * @param context Context to register Maps in
+     */
+    void init(QQmlContext* context);
+
+private:
+    /**
+     * @brief Calculates ratio from reference screen size and size of the current primary screen and inits member mRatio
+     */
+    void calculateAndSetRatio();
+    /**
+     * @brief Initializes map containing all sizes (e.g., button or delegate sizes)
+     */
+    void initStyleSizes();
+    /**
+     * @brief Initializes map containing all spacings
+     */
+    void initSpacings();
+    /**
+     * @brief Initializes map containing all margins
+     */
+    void initMargins();
+    /**
+     * @brief Initializes map containing all paddings
+     */
+    void initPaddings();
+    /**
+     * @brief Scales the value with calculated ratio and inserts it into the given map under the given key
+     * @param map Map to insert key-value pair into
+     * @param key Key used in the map. This is the name used to retrieve the value in QML
+     * @param value Unscaled value
+     * @see mRatio
+     *
+     * In QML the value with the key "defaulSpacing" in the Map "StyleSpacings" is accessed by StyleSpacings.defaultSpacing
+     */
+    void scaleAndInsert(QQmlPropertyMap* map, const QString& key, int value);
+    /**
+     * @brief Applys ratio to given size
+     * @param size Size to be scaled
+     * @return scaled size
+     * @see mRatio
+     */
+    int applyRatio(int size) const;
+
+    qreal mRatio = 1.0;
+    QQmlPropertyMap* mStyleSizes = nullptr;
+    QQmlPropertyMap* mMargins = nullptr;
+    QQmlPropertyMap* mSpacings = nullptr;
+    QQmlPropertyMap* mPaddings = nullptr;
+};
+
+#endif // STYLEHANDLING_H