Twitter bootstrap integration - issue #14

Addresses #14, also preparation for the new study-curation UI. This includes Twitter Bootstrap v2.3.2 and its responsive grid, for graceful adaptation to mobile devices and other small screens.

I've adapted the main ```layout.html``` template and deleted the ```layout_right_sidebar.html``` template, which is no longer needed. I tweaked the main nav-menu to use Bootstrap markup and behavior. __NOTE that most of this menu is now defined statically in ```layout.html```. If this menu has important variations, we might need to adapt web2py's ```MENU( )``` function to restore dynamic menus.__

Future branding (of standalone phylografter, or forked instances) can be done using ```less```; for details, see ```less/README.md``` and notes in the https://github.com/OpenTreeOfLife/opentree project.