tiny readability fixes arising from a11y audit

[StephDriver]

During screenreader testing (#4194) these small readability issues were found:

OLH Theme - Sample 1 Material Theme - [Sample 2] (https://www.glossa-journal.org/article/id/10082/) Clean Theme - Sample 3

• [user content] OLH: Research Articles as if a heading, but it is a single article on the page. Should be singular and a heading.
• [x] Material: Heading Download is ambiguous, 'Download Article' would be preferable.
• [x] Clean: Harvard-Style Citation should be Harvard-style Citation. The only the first word of a hyphen joining should be capitalised.
• [user content] Clean: in the footer published by Open Library of Humanities according to new OLH style-guides there should be the definite article, so published by the Open Library of Humanities.
• [fixed elsewhere ] Clean: in the footer Login> should be Login
• [ fixed elsewhere ] Clean homepage: the use of [...] at the end of a news article summary sets up an expectation of a link, but this is plain text. Either make it a link, or ... without the square brackets.
• [x] for all the above, check for other instances of similar and fix alongside.