Add seven organisations to Powered By

[justinmclean]

Adds AWeber, Apache Camel, CocoIndex, SeaQL, Sockudo, Security Union, and RusTok, each written from the organisation's own public repository, with the source and the date checked recorded in the file.

Only Camel carries a use-case description on the page. The other six have one in their file, but it isn't published, because we wrote it from public code rather than getting it from them. That's what the new showText flag does: it defaults to true, so every existing entry is unaffected, and setting it to false keeps a description in the file without putting words in someone's mouth on the page.

Two presentation fixes came out of adding logos of different shapes. The wall pinned every logo to a fixed height, which left square marks a third the size of the wordmarks, so it now uses a max-height and max-width box instead. Tile spacing went up to match, since a wide logo could previously run to the edge of its tile.

Also widens the section intro so it stops wrapping early and stops "Apache Iggy" from splitting across lines.