Quick fix for two rows of tabs appearing when editing a product

When you edit a product, we currently get a row of two tabs since the tabs can't be placed on a single row. In the end, this problem has to be fixed in the code showing tabs, but in order to fix this situation for the shop module now, I propose we:

• show the title "Edit product" in the dialog header (should be there any way, but also gives context for the tabs below).
• rename the tabs "details","categories","pricing","weight + size"
• we merge the "keywords" with the "categories" tab: the labels for the two fields could be:
  • "product categories" (as we currently do already)
  • "additional keywords" or simply "keywords"

I've added a mockup to this issue to visualize these changes.