Improve consistency of Primary and Marginal forms

[jamespstrachan]

(from Paul's comment on related ticket)

It would be good if we could also bulk assign "primary" or "marginal" to a selection of entries. I noticed this has not always been assigned systematically and I'm not entirely sure what the original designers had in mind, other than trying to add as much information as possible.

I'm currently trying to do some dialectometry based on our datasets/features in the database, but for this, we can base groupings for map displays on only one primary entry/value per location/dialect. If two are equally relevant, this becomes a problem: you'd have to have a square or circle that is split into two colours. It would have been better if the values had been systematically based on lexemes, as in section 17, but they have not. At any rate, it would be good if:

(A) If a dialect has only one entry, this is automatically "primary".
(B) In the user interface, we can Instantly recognize which entry is primary.
(C) We can assign "primary" or "marginal" status to a selection of entries.

[jamespstrachan]

@Paul32N I have moved this to it's own ticket as it's out of scope for #127

[Paul32N]

That's great. So, what do you think of this?