ENH: add linkahead theme

build.properties.d/50.linkahead.conf

src/core/css/linkahead.css

src/core/pics/bg_OxHPDs4WV8Y.jpg

src/core/pics/bg_WDbuusPOnkM.jpg

src/core/pics/bg_kCrrUx7US04.jpg

src/core/pics/bg_txQT60OPSwA.jpg

src/core/pics/caosdb_logo_medium.png

src/core/pics/linkahead_icon_64.png

src/core/pics/logo_indiscale.101x25.png

src/core/pics/logo_indiscale.162x40.png

src/core/pics/logo_indiscale_no_subtitle_218x35.png

src/core/pics/logo_indiscale_no_subtitle_dark_bg_156x25.png

src/core/pics/logo_indiscale_no_subtitle_dark_bg_250x40.png

src/core/pics/logo_linkahead_no_subtitle_144x25.png

src/core/pics/logo_linkahead_no_subtitle_231x40.png

src/core/pics/logo_linkahead_no_subtitle_dark_bg_144x25.png

src/core/pics/logo_linkahead_no_subtitle_dark_bg_231x40.png

src/core/pics/logo_linkahead_no_subtitle_dark_bg_261x35.png

...s/logo_linkahead_no_subtitle_dark_bg_large_font_75x10.png

src/core/pics/tile.png