Make it simpler to change the wiki logo

At the moment the flow to change a logo is clearly difficult since you have to :
1. Go in the ColourTheme administration
2. Edit the ongoing ColourTheme
3. Cancel
4. Attach an image to the ColourTheme page
5. Go back in edit mode on the COlourTheme
6. Pick the attachment name
7. Save

Why not having an upload attachment picker directly in the ColourTheme edit mode in order to have :
1. Go in the ColourTheme administration
2. Clic Browse to pick an image on your computer or in the existing ones in having previews
3. Save