Print status and error messages while importing

[wincohi]

To the user, it may be confusing to see no feedback when attempting to import notes or favicons, especially so if something goes wrong. We should keep the user updated on the following events:

• Parsing begun
• Ready for import (already handled with the enabling of the Import button)
• Import finished (success or failure)

Additionally, we should warn the user in the following situations:

• No notes or favicons (depending on selection) to import
• Some notes or favicons couldn't be imported (due to #18)