Use icon tabs and new navigation buttons to restructure the register object view

aleksis/apps/alsijil/static/css/alsijil/lesson.css

...apps/alsijil/templates/alsijil/class_register/lesson.html

...ps/alsijil/templates/alsijil/partials/lesson/heading.html

.../alsijil/templates/alsijil/partials/lesson/prev_next.html

...templates/alsijil/partials/lesson/tabs/documentation.html

.../alsijil/templates/alsijil/partials/lesson/tabs/more.html

...alsijil/templates/alsijil/partials/lesson/tabs/notes.html

...mplates/alsijil/partials/lesson/tabs/previous_lesson.html

.../alsijil/templates/alsijil/partials/lesson_prev_next.html