Add Kittygram to the frontends

[rootful]

Kittygram is a frontend for Instagram, similar to Proxigram and now discontinued Bibliogram. Would be nice if Fastside supported it.

[cofob]

Hi, implemented in #38.

By the way, I would love to see fastside hosted on fsky :)

[cofob]

Oh, I think I overengineered search string validation and it's broken...

[rootful]

By the way, I would love to see fastside hosted on fsky :)

I've considered hosting it, I'll see what the other admin thinks about it. An FSKY Fastside instance could happen soon. Thanks a lot for adding Kittygram to Fastside!