Added public files

Roughly added all public files. Probably missed some, though.
diff --git a/doc/materials/groups/MATGROUP_FLUID b/doc/materials/groups/MATGROUP_FLUID
new file mode 100644
index 0000000..13f74f6
--- /dev/null
+++ b/doc/materials/groups/MATGROUP_FLUID
@@ -0,0 +1,5 @@
+Gruppenid:
+MATGROUP_FLUID
+
+Name:
+Fluessigkeiten