make settings page

[adam-ce]

• [x] design qml page for settings (for now frame limitter + lod resolution)
• [ ] wire up with qsettings (test persistence on android)
• [x] wire up with renderer

[adam-ce]

think about where to read/write qsettings (probably there is best practise):

• we don't want to pollute nucleus and gl_engine with qsettings (separation of concerns, dependencies)
• qsettings has no notification, so can't set on settings page and let qsettings notify objects => settings page needs to notify objects / set directly
• can't write in destructors (apps are often killed spontaneously)

[adam-ce]

there is possibility of crashing settings (e.g. number of GPU cached tiles later on). think about how to handle that more or less gracefully.

[GeraldKimmersdorfer]

I used qsettings inside the new AppSettings class. It is currently commented out though, because:

• it just saves the frontend settings (datetime, quality, ...) but not for example the gl configuration
• it is confusing and i like to start with a clean slate whenever i start the app (at least on desktop)

For the android app it might be a good idea though!

[adam-ce]

you have a good point with the clean slate. that could be a command line parameter, or a build parameter.