MonitoringDataStorage: permanent folder in ctor

Changed the implementation of: public MonitoringDataStorage(String targetDir, long maxTotalSize, long daysToKeep).
The previous implementation created a temporary folder as targetPath. The folder name was prefixed by the string provided as the first argument of the constructor. The actual implementation uses this argument as the path to the permanent folder representing the targetPath. Therefore, this commit changes the semantic of the above mentioned constructor. However, this constructor has been used until now in only one project - the one actually requiring this change. Using a fixed folder instead of creating a new temporary folder at each startup is desired, because the application will not pollute the file system with lots of folders. At least 3 other constructors (including the parameterless one) can be still used to create the targetPath as a temporary folder.