Added navbar-right class prop to Nav component

Nav components need `navbar-right` classes for dropdown menus to appropriately shift. As it stands, using `pull-right` and the corresponding `pullRight` prop, dropdown menus go offscreen. This makes `pullRight` redundant, but I have kept it for compatibility purposes.

The bootstrap CSS that makes this important ([Source](https://github.com/twbs/bootstrap/blob/35f09315ed543a0479719afa2143240952c215db/less/dropdowns.less#L203)):
```
.navbar-right .dropdown-menu {
  right: 0;
  left: auto;
}
```