Add untrust ipc method

[maidh91]

Context

• We would like doctor to test TrustDialog for new key
• To do that, we need to untrust the key first
• Then click/run on the key again
• The TrustDialog should open

Related PRs

• Add untrust method to pear-ipc: Add untrust ipc method #16
• Add untrust method to pear sidecar: Extend the handler of the option --unsafe-clear-preferences to clear both preferences and permits pear#356
• Add test section to pear-doctor: TODO