Minor tweaks and bug fixes; support for some future integration with other applications.

• Dock and menu bar indication of tunnel activation/deactivation & active tunnel count. Both default to on; see "Preferences -> Interface" to change.
• Redesigned preferences window.
• Tunnels and accounts can now be duplicated for easier editing.
• Contextual (i.e., right-click) menu added to tunnels and accounts in main window (edit, duplicate, and delete tunnels and accounts; activate/deactivate tunnels).
• When selecting agent authentication for an account, Meerkat automatically tries to find (in order) ~/.ssh/id_dsa, ~/.ssh/id_rsa, and ~/.ssh/identity for use as the private key.
• When saving an account, the user is prompted to create a tunnel if none exist (globally, not just for this account).
• When saving an account, the user is prompted to restart all active tunnels on that account.
• Added a credits page.

• Double-clicking a tunnel or account table column header no longer edits the highlighted tunnel or account.
• Saving a new or edited tunnel no longer automatically restarts other active tunnels on the same account.
• Active tunnels are properly deactivated before deletion, including when deleted as a result of an account deletion.
• Quitting in demo mode no longer ignores the "remember window visibility" preference.
• No longer try to activate an already active tunnel. This was occasionally causing conflicting port warnings.
• Fixed missing app icon on the password prompt dialogs.
• Now properly disable the "Registration..." menu item when app is in a modal state.
• Tunnels & accounts automatically re-sort after saving a new tunnel or account.