UI changes including sticky footer and user's tab display

commit 95702446bb341e252c32ae8536def93cf77dc571

    base: visual fix of the user's tab on the header
    
    Signed-off-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>

commit e10d5803c4f18811596b5c0177704f8695dd4c9e

    base: sticky footer fix
    
    * Fixes sticky footer issue on pages with content longer than
      100% window size, by updating to the reference sticky footer
      implementation for Bootstrap3.
    
    * Uses LESS `@import (reference)` to import external files, but
      without adding the imported styles to the compiled output
      unless referenced.
    
    Signed-off-by: Georgios Kokosioulis <georgios.kokosioulis@cern.ch>