Update to iOS 13, use SF Symbols, fixed deprecations, version bump

Merge pull request #96 from bufferapp/task/update-pinremoteimage

Task/update pinremoteimage

Merge pull request #94 from bufferapp/task/some-cleanup

Some clean up

Merge pull request #88 from bufferapp/task/misc-improvements

Centralize initializer

GIF backloading fix

Support gifs for backloading

Merge pull request #85 from bufferapp/task/gif-misc-tweaks

Task/gif misc tweaks

Rolled our own progress indicator

Merge pull request #75 from danielgindi/master

Expose some features for external use

Fix presented view's bounds being changed on rotation