Established settings mechanism

Allows reading and writing default serial port and baudrate (this also is available via the web interface) and setting the host and port on which the server should listen. Might allow persisting more options in the future.

The configuration file is stored in ~/.printerwebui/config.ini under Linux, in %APPDATA%/PrinterWebUI/config.ini under Windows and should be stored in ~/Library/Application Support/config.ini under MacOS X

Closes #1