New features

Added image management. Pressing [1] from the container screen changes dry to the images screen.

Image screen has the same layout as the container screen but the the list of images reported by Docker is shown and commands change:

• [E] Removes the selected image.
• [I] Shows history of the selected image.
• [Enter] Inspects the selected image.

All commands on images have the same behaviour as the official Docker CLI.

Also, first PR merged (#7), to solve #6. Kudos to @hako. Installation script has not been updated yet, so ARM binaries should still be downloaded directly.