Move Sign individual challenges to ce-cli

[sedula27]

[rohit-joy]

Suggestion for the command structure:

ce iir challenge sign --challengeFile challenge.json --key zABC... // outputs signed-challenge.jwt
ce iir challenge verify signed-challenge.jwt // Success/Failure message
ce iir challenge create did:web:example.org // outputs challenge.json

[sedula27]

Updated command structure

[rohit-joy]

This iteration is good! Let's keep the ce login and ce logout as easy to use aliases of ce account login and ce account logout.

[rohit-joy]

Approved with suggestions.