frontpage overhaule, more bootstrap

a new layout file
removed custom menu stuff
try to make 100% bootstrap, hopefully better theming possibilities
hack for anchors in top
better breadcrump links in user manual
rest of changes ...
dutch translation of frontpage
handled suggestions from several people
inserted section for identify features
added the frontpage to the other main entrance pages
Added Ashtun
addition of QGIS maps from flickr
Merge branch 'master' of github.com:qgis/QGIS-Documentation
fixing wrong margin for code examples