Issue 5 health function

[elpiel]

Part of #5

• is_finalized()
• get_status (needs testing)
• is_offline (needs testing)
• Cache::finalize_campaign
• bugfix Cache::initialize
• SentryApi::get_last_approved
• httptest setup

[simzzz]

Looks good, will test thoroughly when I implement the next few functions.

[elpiel]

I am merging this one as it became too big, I will add tasks to #5 to account for the missing tests, etc.