Link Support: target and rel attributes

When working with some of the special components that take to or href attributes (basically components using the link mixin), there isn’t support for passing down the target and rel attributes.

I would love it if the default prop value for rel was rel="noopener noreferrer" to add a security-boosting default per this article: https://www.jitbit.com/alexblog/256-targetblank---the-most-underestimated-vulnerability-ever/. Maybe that could be triggered with a computed property so it only kicks in if a target other than _self is specified.

<template>
    <b-navbar toggleable
              type="inverse"
              variant="primary">
        <b-nav is-nav-bar>
            <b-nav-item :href="FACEBOOK"
                        target="_blank"
                        rel="noopener noreferrer">
                <i class="fa fa-fw fa-facebook"></i>
            </b-nav-item>
        </b-nav>
    </b-navbar>
</template>

[tmorehouse]

Rather than putting too much logic into the component, we could just provide new props (target and rel) to the link component(s), and rely on the user assigning values appropriately for their use case.

[alexsasharegan]

Maybe we should try to keep this on the PR. I’m getting dizzy!