Release 2.7.0

@mattst88 @mcatanzaro I know you guys have been waiting for a new Geoclue release, sorry for the delay.

I think we should still get !141 (merged) in before making the new release since it's important piece of functionality and it's very close to being merged - what do you think @tpikonen?

Proposed draft NEWS changelog (assuming that !141 (merged) ultimately gets merged):

* Multiple config files named *.conf are now read from the config directory at @sysconfdir@/geoclue/conf.d,
* HTTP requests are now made via libsoup3.0 instead of libsoup2.4,
* A static location can now be set in @sysconfdir@/geolocation for immobile systems,
* MLS requests are now submitted with combined WiFi and 3GPP tower data,
* MLS now checks connectivity in a way that allows location and submission servers running on localhost,
* MLS submissions are now made using /v2/geosubmit API,
* MLS cell tower submissions now have the correct radio type,
* MLS requests now submit the BSS age property,
* MLS submissions now contain the location speed,
* MLS cache now respects WiFi signal tolerance strictly,
* NMEA source now supports both '\n' and '\r' NMEA delimiters,
* NMEA source can now be made the MLS submit source,
* ModemManager now use signaled calls to get cached location information to avoid performing explicit modem query,
* Location description now contains information about its source,
* GSettings backend no longer complains about being run from a read-only filesystem,
* Many small improvements and fixes, some memory safety related.

I hope I didn't miss any other notable change - if anyone wants to add something feel free to do this.