Correct errors in 1Password.xcasset since 1.0.9

New images for Retina HD displays were added in e59ae1eca7fd508649aae4394fcc316fc1a1dbd4, but the 1Password.xcasset was not updated. This created numerous warnings. In addition, some existing files were renamed in the repo, but the references to those files were not updated in 1Password.xcasset. This pull request fixes those issues.

In addition, the unused @3x asset for future iPads (?) has been removed. Having this asset in 1Password.xcasset creates a warning on every build. Please wait until this hardware has been released and is supported in Xcode before re-adding.