EDUtest chatcommands

This fork introduces the following changes:

• student privilege disabled to make all non-teacher users 'students' by default
• teacher privilege changed to instructor to avoid conflict with Sfan5's teaching mod
• added chat command heal <subject> to help classes work in enable_damage=on environments
• added chat command announce <message> which displays message in a custom formspec

The goal of the EDUtest project is to facilitate the usage of Minetest in an educational context.

This mod provides chatcommands for the educational staff.

setup

The commands expect the students to be marked with the "student" privilege, while the teacher(s) are marked with the "teacher" privilege.

A common way to set this up would be to add "student" to the default_privs server configuration option, and to revoke it manually from the teacher(s), while granting them the "teacher" privilege.