Misleading error message was shown when a watching wallet is imported repeatedly.

[Keith-CY]

When a wallet is imported repeatedly, Neuron will lead users to replace the existing one.

But if the imported wallet is a watch wallet, Neuron displays an error message of "Invalid JSON file, please check your file integrity", which is misleading.

Expected to show a clearer message. e.g.

1. Watch wallet detected in Neuron: The watch wallet has been imported before, would you replace it?
2. Original wallet detected in Neuron: // TODO

[Danie0918]

• Requirement:

1. Watch wallet detected in Neuron: Click 'Yes' to replace the existing watch wallet, click 'No' to close the popup and cancel the import.
2. Original wallet detected in Neuron: Click 'OK' to close the popup and cancel the import.

[devchenyan]

nervosnetwork/neuron#3214