Add bower.json overrides for bootstrap (#338)

[jaromero]

This addresses #338 as an alternative to ecf4928 by populating bower.json with either of these, depending on whether sass is selected or not, thus allowing us to keep bootstrap up-to-date.

"overrides":
  "bootstrap-sass": {
    "main": [
      "assets/stylesheets/_bootstrap.scss",
      "assets/fonts/bootstrap/*",
      "assets/javascripts/bootstrap.js"
    ]
  }
}

"overrides":
  "bootstrap": {
    "main": [
      "less/bootstrap.less",
      "dist/css/bootstrap.css",
      "dist/js/bootstrap.js",
      "dist/fonts/*"
    ]
  }
}

I could not figure out a way to test the actual result of the fonts task, so the test just checks whether the font paths are present in bower.json.

This should be a temporary measure until this issue is resolved and bootstrap also updates accordingly.

[silvenon]

It works! Could you just update Bootstrap dependencies to ~3.3.5? (And squash it into this commit.)

[jaromero]

Done, and done.

[silvenon]

Awesome! Thanks 👍