Updating the downloads page:

- some phrasing fixes
- distinct between mana and manaplus downloads
- add downloads to some manaplus versions, especially the MAC versions
Fixes based on bjorn's feedback.

There's still the open quest whether to remove the direct download links
(and see about the branding)
and only link to the download pages of mana and manaplus.
More updates on the downloads page:

- Add link to tmw-branded manaplus.
- Re-add link to tmw-branded mana 0.6.0.
- Mark Windows Portable as mana based.
- Add link to manaplus android app.
Merge pull request #2 from jtoelke/master

Updating the downloads page