Rejig rule table

[Fweddi]

What does this change?

Apologies for the one commit - Git wreaked havoc on my commit history, and I haven't the heart to go back over my commits and rebase.

This PR tweaks the order of the fields -> "Description", "Pattern", "Replacement" in the form, and in the table. We feel the order should be like this because:

• Description best describes a rule, and is always present
• Match is always present, and reading left to right from ‘match’ to ‘replacement’ makes sense
• Replacement is not always present

We have also renamed some fields, and added some handling for empty fields (here we now display 'em dash': –)

How to test

Is the form and table more consistent? Do the changes make sense?

[Fweddi]

Looks good. Worth making our – 'subdued? At the moment, impossible to distinguish between a field that contains that character.

I tried it with subdued and lightShade - both were far too light to make out. Could try another colour if you want, but I'd like to think that it's very unlikely any of our fields will consist of a single em dash!