[Bug] Media query and classes rendering issue

Hi,

I was trying to make a responsive layout but I discovered that the device switcher does not work consistently. The issue can be replicated in the official demo.

Open http://grapesjs.com/demo.html Keep the "Desktop" as the selected device. Add at the top of the "Header" 2 block of type "2 Columns" (just above the menu). Select the first "Row" inserted and set its padding-left to 100px. Select the second "Row" inserted and set its padding-left to 100px. Switch to the device "Tablet". Add the class "np" to the selected "Row" (switching the device does not deselect it) and change its padding to 10px. Select the first "Row" and add the class np.

The rendered padding-left is not updated, it is 100px, while I expect it to become 10. NOT good.

Switch the device to "Desktop", the padding-left of both rows is 100px. Good. Switch the device to "Tablet", the padding-left of both rows is 10px. Good. Switching multiple times all the devices the padding-left is updated correctly. Good.

Another example.

Open http://grapesjs.com/demo.html Keep the "Desktop" as the selected device. Add at the top of the "Header" 2 block of type "2 Columns" (just above the menu). Select the first "Row" inserted and set its padding-left to 100px. Select the second "Row" inserted and set its padding-left to 100px. Switch to the device "Tablet". Add the class "np" to the selected "Row" (switching the device does not deselect it) and change its padding to 10px. Select the first "Row" and add the class np.

The rendered padding-left is not updated, it is 100px, while I expect it to become 10.

Switch the device to "Smartphone", the padding-left of both rows is 100px. NOT Good. Switch the device to "Tablet", the padding-left of both rows is 10px. Good. Switch the device to "Desktop", the padding-left of both rows is 10px. NOT Good. Switching multiple time does not solve the issue. NOT Good.