Implement Properties Editor as a customizable dock

The Idea here is to make the properties editor act more like a docker in typical graphics programs eg. Photoshop/Affinity. by doing this, we could make more panels accessible in a more efficient way, for example separating scene management tabs from object properties tabs into separate 'banks' of tabs makes for a cleaner and more logical layout. Like in photoshop, clicking in a tab expands the area for better access, so that its not necessary to manually expand the outliner when you need more space, and then shrinking it to get at the object properties.A quick MMB click will minimize a bank of tabs, giving the others working space, but are a single click away when you need them. A drop down menu can contain more rarely needed panels, layout options, as well as tab specific menus, for example outliner or layer manager sorting options. tabs can be drag and drop, split into separate banks and recombined. the beauty of this is that it's completely customize-able to any workflow, if a user wants it to work like it is now, he can simply split the editor and edit the layout as he wishes. the layout can also be tied in with the work-space presets, so that when in a task specific workspace, we can do away with unrelated panels for a cleaner UI. I made mockup GIF to demo the concept, ignore that drivers panel, I was using it to demo how we could enable additional panels, but its probably not a good example, better ideas could be a layer manager, asset browser, or texture/materials manager. This link here has some good mockups for layer and asset management tabs, but implemented in a more limited way - outliner editor only. wiki.blender.org/index.php/User:Axelmening