Foursquare was rebranded Swarm (for check-ins) some time ago, so
rename our implementation to match the upstream branding. But still
store "foursquare" as the permanode importer type, to not break old
users. That override is now added to the new Properties struct, and
all importers now return their properties.
More stuff will be added to Properties later: WIP flag, bug link,
proper title, icon?
Change-Id: I31cbe2feec3dbf9c6bdb0c866056d9c6966313e3
Brad Fitzpatrick