Custom toolbar

I want to add some custom into the toolbar but I found the entire process really cumbersome and not intuitive.
For example in the main toolbar I've added a "tool window" and a "database" button but:

- they don't appear with their default icons. 
- you can't edit the icon for "tool window", the edit action button is greyed out
- I can edit the icon for the "databse" button but I've no clue where is the icons folder (searched and googled), I just want to use the same phpstorm icons, where are they? 
- most important: database button (and other buttons from the database plugin) doesn't even appear on the toolbar! I can't find a way to swiftly open the database tool without navigating in the menu view->tool windows->database