Upgrade to LVGL 8

[Riksu9000]

• Button behaviour while sliding finger has been improved. Now pressing on one button, sliding to another button and releasing will activate the first button rather than the second. Still not perfect but better than before. Relevant after #492
• disp_drv->full_refresh = 1 Can be used instead of backgroundLabels to force full refresh. This can also be done in LVGL 7 #1100
• Handling events has been made easier by making it possible to pick only the events we want. No more if (event != LV_EVENT_CLICKED) needed.
• Objects are realigned automatically.
• Bar styling has been improved, which I can see as being useful for prettifying the UI. Maybe there are more useful styling updates.

Seems like this update would make coding easier and reduce weirdness.

https://blog.lvgl.io/2021-06-01/release_v8.0.0

[Avamander]

How's the performance?

We also haven't yet made it to using flash resources, so work done on that might conflict with upgrading LVGLv8.

I guess it would be better to choose which should be done first, if we want to upgrade now at all.

[Quantum-cross]

I'm very interested in working on this :)

I will probably start messing with it soon.