SWZ: add git submodules pointing to our clones of the frbatlanta repositories

.gitmodules

+[submodule "ms-sbvar/utilities_dw"]
+	path = ms-sbvar/utilities_dw
+	url = http://www.dynare.org/git/frbatlanta/utilities_dw.git
+[submodule "ms-sbvar/TZcode"]
+	path = ms-sbvar/TZcode
+	url = http://www.dynare.org/git/frbatlanta/TZcode.git
+[submodule "ms-sbvar/switch_dw"]
+	path = ms-sbvar/switch_dw
+	url = http://www.dynare.org/git/frbatlanta/switch_dw.git

TZcode @ 9a5fc001

+Subproject commit 9a5fc0011e46655dffb9edc58411a32a319cc0cc

switch_dw @ 02eb0b2e

+Subproject commit 02eb0b2e3b357c34eb76602449242cdc353694b4

utilities_dw @ 83a68e13

+Subproject commit 83a68e131f62f2544b550d6e5927f97cf75d1b23