Improve Flagging Individual Subjects on the Mobile App

[wgranger]

A user brought up a good point on a talk post about wanting to mark individual subjects in the mobile app they thought were interesting. Building out a sort of "wow" button is a stretch since that doesn't exist anywhere in the Zooniverse, but we could discuss bringing in the favorite button or done and talk functionality into the mobile app? Basically, a way for users to come back and see interesting subjects.

This is definitely an enhancement, as this isn't the main priority for mobile currently. This is particularly a challenge on mobile with such little real estate. Tagging @beckyrother

[beckyrother]

We started to work on this earlier this year: https://projects.invisionapp.com/d/main#/console/13393648/333632079/preview

[beckyrother]

Adding a Favorite button at the bottom of the image and a tab in the hamburger menu to see all Favorites. Still needs some work but that's where we're at at the moment