InfiniTime "Green avocado" - LVGL update

This release updates the version of LVGL (LittleVGL) from version 6 to version 7. This is a major update that brings many improvement and update that have been made in the LVGL project.
I know that several contributors were waiting for this update to create new watchfaces and apps, and I hope they'll unleash their creativity now that it's finally there!

I would like to say a bit thank you to Joaquimorg for this contribution. Joaquimorg maintains his own fork of Infinitime and did a great work to port this update into InfiniTime, adapting all the apps and improving the theme used in InfiniTime!

Thanks also to roblabla for fixing the CMake FLASH target !

And also thanks to Nico for initiating the idea to name InfiniTime releases !