TagCommander background measurements

• TagCommander measurements are now performed in background. This is especially useful for heartbeats (uptime and pos) sent during background playback.
• When using the SRGAnalytics_DataProvider.framework companion framework, and for resources equivalently fitting the same set of playback settings, HTTPS resources will be preferred over HTTP resources. Previously, depending on the (unreliable) order of such resources, playback would either occur over HTTP or HTTPS, which could lead to seemingly random failures if App Transport Security was not allowing HTTP playback.