update logo images

src/main/webapp/images/admin/logo-top.gif

src/main/webapp/images/logo-head.gif

src/main/webapp/images/logo-head.png

src/main/webapp/images/logo-mono-nega.png

src/main/webapp/images/logo-mono.png

src/main/webapp/images/logo-small.gif

src/main/webapp/images/logo-small.png

src/main/webapp/images/logo-small.xcf

src/main/webapp/images/logo-top.gif

src/main/webapp/images/logo-top.xcf

src/main/webapp/images/logo.gif

src/main/webapp/images/logo.png

src/main/webapp/images/logo.xcf