Allow for table borders on row and cells

[ashley-hebler]

What's this PR do?

Right now, the class c-table--bordered applies a row (top/bottom) border, but this changes that to apply both row and cell (left/right) borders.

This also documents the recommended markup for sorted column headers

Classes added (if any)

-.c-table--bordered-rows- For case where you just want row borders

Why are we doing this? How does it help us?

Used for directory

How should this be manually tested?

npm run dev

See: c-table

Does this introduce a breaking change where queso-ui is used in the wild? If so, is there a relevant branch/PR to accompany this release?

I've been sorta walking back on my initial interpretation of what merits a major release. I think instead of anything that introduces a visual change, it should be anything that introduces visual disruption. In this example, this PR will make this c-table--bordered instance suddenly have borders on all sides if versioned up, but I don't consider that to be disruptive or breaking. My intention is to prevent us from just having a ton of major releases that become daunting to update. I think as long as release notes warn about any subtle style changes, that should be an ok safeguard. I updated the contributing guideline to clarify that.

For those ^ reasons, this will be a minor pre-release to be tested out in the directory feature branches we're working on.

TODOs / next steps:

• your TODO here