Tattoo enhance

Use OCP namespace + use img instead of css for displaying background.

With css, the background image is "cut" by other div (for example, you may not see the background image in the files list if there is too many file rows).
I use an img, with position absolute, bottom right like the css background, z-index and small opacity to prevent visibility problems.

This includes the patches from issue #857 since they fix broken things in tatto app for ownCloud 5