Per-channel analytics should require auth, fixes #287

[Ivshti]

The channel analytics now require that the channel creator (advertiser) authenticates.

This fixes 3 distinct issues:

• analytics: channel-level stats should require auth #287: advertiser analytics per channel must require auth
• calling this path with authentication actually caused earning (publisher) stats to be retrieved for this channel - leading to zero results for almost all channels except the one where the creator is both an advertiser and publisher
• calling this path with authentication will cause it to be cached in the same cache key as every other call to it, leading to results for different callers being served