Update website to be more mobile friendly & use Bootstrap 3

[pgleeson]

Currently the openworm homepage (and rest of www.openworm.org) looks quite bad on mobile:

This is probably down to the version of Bootstrap used. An update to v3.x will help, but may break other things...

This may help: https://code.divshot.com/bootstrap3_upgrader/

• [x] Upgrade underlying javascript libraries to reasonably current versions for future proofing (Bootstrap, FontAwesome if necessary)
• [ ] Address certificates issue with github hosting so OpenWorm.org comes up with no security errors
• [x] Menubar at the top is currently black on black; make sure it is visible on mobile
• [x] On pages like donate page, the menubar is obscured / overlapped by the green header box
• [x] Donate header text should just point to donate page
• [x] Images in carousel should not look squashed (aspect ratio)
• [x] Left / right arrows in carousel are invisible on some panels (green background box)
• [x] Donate button on donate page extends width of entire page -- fix so it shrinks to fit the width rather than extending the width of everything else

[pgleeson]

Done with #163. Moving last item to new issue #164