Page titles need to be unique and descriptive

[garcialo]

I noticed that the page titles don't describe the pages even though there are unique and descriptive title variables set in the markdown for each page.

We should at the very least be using the title variables unique to each page. Some of the title variables should be updated.

Here are suggestions for <title> elements for each page.
ex. Page Name, Page Title

Home, Justice Democrats
About, About - Justice Democrats
Policies, Policies - Justice Democrats
Candidates, Candidates - Justice Democrats
Join, Join - Justice Democrats

It would be nice to follow a similar pattern for the shop and other pages on the justicedemocrats.com domain.

Note: Might also be a good idea to change the URL of the Policies page from "/issues" to "/policies"

Rationale:
Screen reader users rely on the page title being read out as they navigate windows or tabs.