Update release list on downloads page

[stomar]

The downloads page needs an update. The way the release list is structured has changed. This makes it easier to handle changing numbers of releases in different maintenance phases.
See e8e91bd and 2c353e4.

• bg
• de
• es (@dabit)
• fr (@chikamichi, @chatgris)
• id (@gozali)
• it (@alepore)
• ja (@makimoto)
• ko (@marocchino)
• pl (@crabonature)
• pt
• ru (@gazay)
• tr
• vi (@joneslee85)
• zh_cn (@hlcfan) 770eed8
• zh_tw (@JuanitoFatas) d51d171