View single setting

[robdefeo]

Is your feature request related to a problem? Please describe.
Settings are complex and important in Mailchain, its important to understand what settings are used to see the behavior of the client. A complete list of settings can be viewed using mailchain settings view and flags can be applied to include default values. It is not easy to quickly see a single setting value.

Describe the solution you'd like
Run a command to return a single value.

• add command mailchain settings view [setting] e.g. mailchain settings view server.port
• return the current setting for e.g. server.port
• Return if setting is default value