Less wonky toggle latex fragment

Using the raw `org-toggle-latex-fragment` function creates some havoc
with the overlays, resulting in nonfunctional notebooks.  Add some
custom logic to improve behaviour.

Cask

@@ -19,5 +19,6 @@
  (depends-on "auto-complete")
  (depends-on "company")
  (depends-on "smartrep")
+ (depends-on "px")
  (depends-on "f")
  (depends-on "s"))

lisp/ein-notebook.el

@@ -39,6 +39,7 @@
 (require 'ewoc)
 (require 'mumamo nil t)
 (require 'company nil t)
+(require 'px nil t)
 
 (require 'ein-core)
 (require 'ein-classes)
@@ -211,9 +212,10 @@ Current buffer for these functions is set to the notebook buffer.")
 (ein:deflocal ein:%notebook% nil
   "Buffer local variable to store an instance of `ein:$notebook'.")
 
+(ein:deflocal ein:%notebook-latex-p% nil
+  "Is latex preview toggled")
+
 (define-obsolete-variable-alias 'ein:notebook 'ein:%notebook% "0.1.2")
-
-
 
 ;;; Constructor
 
@@ -511,10 +513,18 @@ notebook buffer."
   'ein:notebook-show-in-shared-output
   'ein:shared-output-show-code-cell-at-point "0.1.2")
 
-(autoload 'org-toggle-latex-fragment "org")
-(defalias 'ein:notebook-toggle-latex-fragment 'org-toggle-latex-fragment
-  "Borrow from org-mode the rendering of latex overlays")
-
+(defsubst ein:notebook-toggle-latex-fragment ()
+  (interactive)
+  (if (featurep 'px)
+      (cl-letf (((symbol-function 'delete-all-overlays) #'ignore)
+                ((symbol-function 'org-remove-latex-fragment-image-overlays) #'ignore))
+        (if ein:%notebook-latex-p%
+            (progn
+              (ein:worksheet-render (ein:worksheet--get-ws-or-error))
+              (setq ein:%notebook-latex-p% nil))
+          (px-preview)
+          (setq ein:%notebook-latex-p% t)))
+    (ein:display-warning "px package not found")))
 
 ;;; Kernel related things