Add util.h and util.cpp

- Some "utility" functions are defined in these files.
Implement util::loadSettings() for LocalCaPso
Delete old commented code in controller.cpp
Make util::loadSettings() return false on error

- It returns false if the settings file cannot be opened or
- It returns false if the settings file cannot be parsed
Show an error message if settings cannot be loaded
Implement util::writeSettings
Change order of parameters of util::writeSettings

- Put "filename" first to avoid unnecessary coding.
Delete old code in Controller::initializeSettings

- Use util::writeSettings instead of the old code.
- Also correct some bad values in the signature of util::writeSettings
Delete non used header files in controller.cpp
Show error message if settings cannot be written
Update LocalSettingsDialog::accept()

- Use util::writeSettings() and remove old code.
Add an error message in LocalSettingsDialog::accept()

- If the settings file cannot be written, show the error.