Improve authentication handling

[frankgiordano]

#178

Secure password better so it can be specified and used without exposing it as plain text within the config.json file.

Following PR request will change the way username and password is processed for each JSON profile connection.

Proposal:

• Make username and password JSON config profile variables optional.
• Prompt username and password at app startup for the first JSON profile hostname connection only if username and password are NOT already specified within the first JSON profile.
• For each first "change" connection item command will prompt for username and password if not specified in its JSON profile.
• For each subsequent "change" connection command, it will use the cached username/password from its first prompt inputs.
• Add Linux like "usermod" command to allow end user to change username/password for the currently defined cache connection settings.
• Disable special key combination features while prompting for username and password.