[print] hide menubar and footer

see http://getbootstrap.com/css/#responsive-utilities-print
make breadcrumbs a macro
add breadcrumbs method
add breadcrumbs to notebook view
fix link to repo listing in tree view
Merge pull request #225 from pierriko/feature-print

[print] hide menubar and footer
Merge pull request #228 from minrk/breadcrumbs

add breadcrumbs to notebook page
Simplify the subtitles.
Merge pull request #232 from ellisonbg/subtitle

Simplify the subtitles on the main page
reduce log level of some common operations

our logs are flooded with cache messages,
which we generally only care about when they are slow.

This demotes most of these to debug-level unless they are slow.
fix debug demotion in log_handler

any 304 should be debug-level, not just static files
add favicon.ico and robots.txt
Merge pull request #233 from minrk/less-logging

reduce log level of some common operations
Use "Notebook Viewer" instead of house icon in header.
Reduce huge jumbotron bottom margin to something more consistent.
Merge pull request #236 from ellisonbg/jumbo-margin

Reduce huge jumbotron bottom margin to something more consistent.
fix front page link to IPython docs
update link to R magic extensin
Merge pull request #237 from Carreau/update-R-link

update link to R magic extension
Rely on 2.0.0 release