Some suggested changes

Hi Pierre-Alexis

I have some suggested changes here. They are in 3 commits for different file types to make it easier to cherry pick if you don't like all of it! In chronological order

1. I added a block of text to the top of the form giving some details so people know what they are filling out. I also changed the title for the manifest to be in lowercase as that is what we want for the filenames.
2. I then reshuffled some of the items in the okh.okhdf file to make an order I found a bit more logical. I also added some alternative names with the <> syntax. It would good to be able to add section headings into this file somehow. (I'll make an issue)
3. I was having trouble using the form on my laptop as I have quite a small screen, so I reduced the banner size in the CSS, and the size of the H2 headings.