Real-time: Send bulk measurements to the API

[Claypuppet]

Current situation:

• At the time of sending, if the API times out / is not available, the measurement will be lost.

Idea:
Option to send bulk measurements to the API at once. This will help with the following

• missed measurement can be sent together with the next
• future optimization: send multiple measurements at once (e.g. once a minute)

@robouden Can you find out which endpoint can be used for bulk posting?

[robouden]

Found this:

https://github.com/Safecast/safecastapi/blob/6cf3612427b8d05c4855d491646f40da74a16987/app/views/home/show.html.erb#L160