Add "Settings" dialog

[roata]

As new functionality is added, we have to add a way to control certain aspects of the software. Here is an enumeration of the things we need so far:

• language selection - choose one from a list of options, currently: Romanian, Russian and English
• dexterity - left-handed vs. right-handed, see Show zoom control #51 for details
• favourite routes - choose one or several routes from the list of available ones, which will be shown by default

As we don't have many settings at the moment, everything fits in the "hamburger" menu. This will be revised later, if the software grows in complexity. Here is a sketch of what it could look like:

[roata]

Go ahead, thanks!