Implementing certificateFile + filename functionality

See merge request !39

Fixing images in README

See merge request !38

Fix drop school

See merge request !40

M3 observability

See merge request !33

M3 data initialization

See merge request !34

# Conflicts:
#   application/module-language-school/src/main/java/org/fuseri/modulelanguageschool/course/Course.java

M2 fix exercise

See merge request !32

M2 fix certificate

See merge request !36

M2 fix language school

See merge request !35