bug #1813: Storage type for BODY columns is now MEDIUMTEXT (this is only relevant for MySQL DBs)

(cherry picked from commit b68a8b6c83bdc6afb88febfb5ce304e57c20dd7b)

Conflicts:
	src/nebula/Nebula.cc
	src/nebula/SystemDB.cc
	src/vnm/VirtualNetwork.cc
bug #1813: Include SystemDB files, now separated from nebula.cc implementation as in 4.x