Streak modal

Summary

Adds a new modal to announce you started a streak if you make a post and your streak is currently 0.

Note: It calls the modal when you SUBMIT a new post, not when the post necessarily goes through successfully and updates your actual streak. So there may be cases where a user submits a post that fails to submit, and gets the modal. Oh well. I think it's still a better user experience to get the streak unlocked as soon as you post and not have to wait for the post to finish submitting, get confirmation, etc, to then randomly have this come up a few seconds later once you already started scrolling started again.

Also: just in case a user somehow triggers this modal but they do already have a streak that's not zero, it WILL show their actual current streak number. This is to avoid someone thinking they lost their streak when they didn't it's just some wrong thing causing the modal to pop off. Rare circumstance probably, but I wanted to account for it to avoid meltdowns.

Screenshots (if appropriate):