Improved landing page

Signed-off-by: Álvaro Arranz <aarranz@conwet.com>
Extend landing page improvements to be usable by all themes
Remove ComputedStyle.js script from js_smartphone_includes
Fix typo: onorientationchange => orientationchange
New class: TaskMonitorModel
Load WirecloudHeader in the landing_page view (now users are able to sign in from the landing page)
Remove unused code