Merge branch 'dev' into 'master'

Implement first versions of file browser, text viewer and image viewer

See merge request bohacfr2/apo-sem!1

refactor: split imageviewer to more functions and files

feat: add image viewer mode indicator

feat: add correct error messages for text viewer and image viewer

refactor: delete unused code

feat: add mzapo sdl

refactor: use libmagic even for ppm

refactor: use libmagic instead of custom handling magic numbers

refactor: cleanup build flags

fix: includes for jpeg

docs: correct formatting

docs: add code documentation

refactor: move gui elements to gui library

refactor: remove irrelevant comment

refactor: move direction to library

feat: add outline for cursor

refactor: add errors to enum

fix: use rpath instead of ld library path

feat: turn on red led on error

feat: turn on ledstrip for cursor position