add all submodules

.gitmodules

@@ -4,3 +4,9 @@
 [submodule "backend"]
 	path = backend
 	url = https://github.com/lesspass/api.git
+[submodule "core"]
+	path = core
+	url = https://github.com/lesspass/core.git
+[submodule "webextension"]
+	path = webextension
+	url = https://github.com/lesspass/webextension.git

core

@@ -0,0 +1 @@
+Subproject commit da233fb253b79e1421848210af7374e73194d182

webextension

@@ -0,0 +1 @@
+Subproject commit 3cf76acbb6647ee91c87e2292da9bc7acde3e35c