Import Bootstrap from npm and upgrade to latest 3.x

[Hirse]

Most changes in bootstrap's minor version upgrades are fixes and security patches. I only found the following changes required for us:

• Replace dropdown .pull-right with .dropdown-menu-right
• Remove white-space from .dropdown-header
• Use new .container-fluid class for wide container

A further upgrade to 4.x is more complicated as it contains lots of breaking changes and switches from LESS to SCSS.

[campersau]

The tests are failing because that apparently wasn't the best idea: https://github.com/FredrikNoren/ungit/blob/a65cbc80595e79d3ac837dcfd23a2e7f8eb82dbc/components/graph/git-node.js#L178

You could replace that with for example this

const textBox = event.currentTarget.parentElement.querySelector('input[type="search"]');

to fix it.