`api_key` should be `project_token`

[tonydewan]

With the expansion of the API we did earlier this year, we consolidated our nomenclature on:

• tokens not keys
• API Token for user's tokens, used for API access
• Project Token for authentication of metric-sending agents

Given that, we should at least change the user-facing bits to be project_token instead of api_key. Ideally, we change all the internal stuff too.

[janxious]

started doing this a bit in #27 but there's more to do