build menu: use faster lightmap writing, reword the entries

• use -fastlightmapsearch light stage option to speed-up light map storage
• use -nobouncestore light stage option to not store lightmap on every bounce
• reword the entries:
  • only useful “Fast” (previously “Test”) entries
  • only good “Final” entries
  • only one single step: minimap
  • drop useless “noSRGB” (“OLD LIGHTING”) entries
  • always start menu entries with Caps
  • reword the entries
  • name file extension as it is produced (lowercase)
  • explain better the -onlyents option

Apply a lot of suggests by @julius__.

Edit: actual screenshot: