Resolve "Name is not updated in menu"

Closes #44

Short description

This changes the way the name and profile picture displayed in the sidebar are retrieved. Instead of downloading a base64 encoding of the image and storing it along with the user's name when the initial login request is sent, it now merely uses a url for the image (since React Native caches images anyway). Also, this url and the user's name are retrieved every time the app is started freshly, causing them to always be up to date.