Add ohif-viewer package to work on sharing components across viewers and test the standalone viewer via script tag

.gitmodules

@@ -0,0 +1,9 @@
+[submodule "Packages-react/ohif-core"]
+	path = Packages-react/ohif-core
+	url = git@github.com:OHIF/ohif-core.git
+[submodule "Packages-react/react-viewerbase"]
+	path = Packages-react/react-viewerbase
+	url = git@github.com:OHIF/react-viewerbase.git
+[submodule "Packages-react/react-cornerstone-viewport"]
+	path = Packages-react/react-cornerstone-viewport
+	url = git@github.com:cornerstonejs/react-cornerstone-viewport.git