Change documentation heading

[ksuderman]

Change headings from Properties to Features in the vocabulary pages.

The code uses a Map named features but the headings in the documentation are "Properties". These should be consistent.

[keighrim]

I think this can be a more complicated problem than just changing the title of the table(s) on the vocab item web page. As per the JSON schema, Annotation object can have @type, id, label, start, end, and features and metadata, so there is a caste that divides between start,end (as first-class citizens) and all other features (dumped in second-class features car).

[marcverhagen]

There is probably no problem here since all this does it update what is printed on the vocabulary html pages. We would still need to clarify this issue in the specifications, but it sounds reasonable to say that the vocabulary defines features, and that in LIF some of those features live on the annotation type and some in the features dictionary.