Cleanup.

- Replace usage of `SecKeychainSearchCreateFromAttributes` with `SecItemCopyMatching` which returns a CFDictionary.
- Fix the failure to get password data back from an object by using a real SecKeychainItemRef instead of searching for it again.
- Implement action validation for Keychains & Keychain Items.
- Adds icons for locked/unlocked keychain, and actions to lock/unlock them.
- Add counterpart actions to get a keychain item account, fixes quicksilver/quicksilver#833.
- Allow getting note contents as a keychain item children.
- Create identifiers on the fly. This fixes browsing items and password data.
- Loads Certificates, Keys, and Identity as well, but there's no action for those.
- Listen to Keychain lock/unlock events to update the icon.
Let the Keychain Access window disappear.
Ensure Keychain icon state is always up to date.
Add documentation.
Some Info.plist tweaks.

- Replace `rankModification` with `precedence`.
- Add QSTypeDefinitions so the object type displays in Actions preferences.
- Comment out `QSKeychainItemShow` as it's not yet implemented, else it appears in the Actions pref pane. Shouldn't it obey `disabled` ?
Merge pull request #2 from tiennou/master

Cleanup