KSPaths writable locations

KSPaths::writableLocation does not use the current application name when determining the filesystem location where it may write data to.

class KSPaths
{
  public:
    static QString locate(QStandardPaths::StandardLocation location, const QString &fileName,
                          QStandardPaths::LocateOptions options = QStandardPaths::LocateFile);
    static QStringList locateAll(QStandardPaths::StandardLocation, const QString &fileNames,
                                 QStandardPaths::LocateOptions options = QStandardPaths::LocateFile);
    static inline QString writableLocation(QStandardPaths::StandardLocation type)
    {
#ifdef Q_OS_ANDROID
        if (type == QStandardPaths::GenericDataLocation) {
            return QStandardPaths::writableLocation(QStandardPaths::AppDataLocation);
        }
#endif
        return QStandardPaths::writableLocation(type) + "/kstars/";
    }
};

There is indeed a special case for Q_OS_ANDROID for QStandardPaths::AppDataLocation as this system will not allow applications to access anything else than what is allowed. Is there any point in doing different for other systems?

Of course, when KSPaths::writableLocation is called with QStandardPaths::GenericDataLocation, we end up with ~/.local/share under linux for instance, and this is not where we should store data. This is probably the reason for the suffix. But in this case, we should not allow to write anything there and use QStandardPaths::AppDataLocation instead.

This also prevents tests from running independently. Catalog data, for instance, is stored in ~/.qttest/share/kstars (QStandardPaths::GenericDataLocation being applied KSPaths::writableLocation), and is the same for all tests. It is therefore not possible to run tests in parallel and expect persistence separation:

    QString dbfile = KSPaths::locate(QStandardPaths::GenericDataLocation, QString("skycomponents.sqlite"));
    if (dbfile.isEmpty())
        dbfile = KSPaths::writableLocation(QStandardPaths::GenericDataLocation) + QString("skycomponents.sqlite");

Same at other places, such as log storage:

    qint64 totalSize = getDirSize(KSPaths::writableLocation(QStandardPaths::GenericDataLocation) + "logs");
    totalSize += getDirSize(KSPaths::writableLocation(QStandardPaths::GenericDataLocation) + "autofocus");

Or Dark Library:

    QDir writableDir;
    writableDir.mkdir(KSPaths::writableLocation(QStandardPaths::GenericDataLocation) + "darks");
    writableDir.mkdir(KSPaths::writableLocation(QStandardPaths::GenericDataLocation) + "defectmaps");

It is actually the same for all KStars modules. Would there be any harm to replace all occurrences of QStandardPaths::GenericDataLocation with QStandardPaths::AppDataLocation when modules call KSPaths::writableLocation?