.gitconfig: Add options and aliases for git submodules

.gitconfig.inc/common.gitconfig

@@ -7,14 +7,24 @@
 [pull]
     ff = only
 
+[push]
+    recurseSubmodules = check
+
+[submodule]
+    recurse = true
+
 [pager]
     branch = false
     config = false
     stash = false
 
+[status]
+    submodulesummary = 1
+
 [diff]
     tool = vimdiff
     guitool = gvimdiff
+    submodule = log
 
 [diff "ansible-vault"]
     textconv = ansible-vault view
@@ -45,3 +55,6 @@
 
     # Reset HEAD to last commit, but keep files as they are
     undo = reset HEAD~1 --mixed
+
+    # Submodule helpers
+    sm-update = submodule update --init --recursive --remote --merge