add options: --no-verify-ssl and --trusted-ca

[abdeldjalil-fellah]

since himalaya is a tls client when starttls/tls is used, these options are needed:

• --no-verify-ssl : to bypass server cert check
• --trusted-ca : to specify custom trusted ca certificates

[soywod]

Adding CLI arguments dedicated to IMAP is not a good approach IMO, because the API is actually backend-agnostic. The right place for such options are in the configuration file, in the .imap section. This may be related to #546, I'm not sure yet how to disable SSL verification with rustls, PR are welcomed.