Dispose large assets as views are unmounted

[jadnco]

In particular the views associated to creating new Spots.

From a stationary standpoint, the app uses ~42MB of memory and ~7% CPU. Those numbers are pretty decent. As the user creates a new Spot this changes quickly.

• Loading up the NewSpotSource view (on the library tab) jumps the memory up to ~72MB, likely because a series of large images are loaded in.
• Clicking and using the Camera view bumps memory up to ~90MB.
• After a photo is taken from the camera or selected from the library, the photo gets passed through to a new view. Memory is now up to ~98MB.
• Moving into the next view, where the user can add a title and caption it's at ~105MB.

I believe the memory is constantly increasing because the large photo assets aren't being disposed of as the views get un-mounted.

This is something that needs to get looked into. Using +100MB is totally fine, it's just not ideal.

[jadnco]

Managed to get this up to 500MB just by traversing through views and loading many images.