Remove space from the heading of 'Download' page

There is a leading space in the heading of the 'Download' page,
i.e. download.html. Remove this leading space.
Add release notes

Create a new page called releases.html to display the release
notes for every release. Update the 'Download' page, i.e.
download.html with a link to the release notes for QuickQWERTY
1.0-beta2. Update the footer of all pages with a link to
the release notes.