Add UI to matched entry card for configuring match preference

[luckyrat]

• Allow matched entries to render differently to non-matched entries - perhaps implicitly via a true/false/undefined flag to indicate if the entry is the current preferred match.
• Add a new row underneath current card contents with a star icon button and label: “Preferred matching entry”
• Tooltip upon hovering over the star icon button: “Make this my preferred entry for this website”
• Clicking the button will behave as described below.

if this entry is the current preferred entry:
1. remove all config settings that can make it the current preferred entry (all Domain, hostname and page settings that specify this entry’s UUID)

else:
1. if another entry is the current preferred entry remove all config settings that can determine the current preferred entry if they are equally or more specific than the configured target
2. create a new “Exact method” per-site setting to record the UUID of the entry using the configured target

* if #276 has not been implemented: configured target = Domain

When removing an existing setting, we’ll either remove just the preferred entry UUID or, if we can determine that no non-default options are in use for the specific site configuration, we can remove the entire per-site configuration for the target and value in question.

[luckyrat]

I'll use a checkbox rather than a star icon since this is more likely to be understood by a larger number of users. Additionally, I think that the checkbox along with the label next to it should provide enough information that the additional noise from a tooltip is unnecessary so I'll skip that part of the design.