Replace Keytar - Store creds in plain text

[JTonda]

Replace keytar by storing credentials in plain text with the other profile information. Ensure python/C++ are no longer required prerequisites to use Zowe CLI. Update documentation.
8 Story Points

• Design Session (Add additional tasks after)
  Status: Complete
  Assigned: @AHumanFromCA
• Run final design by stakeholders
  Status: Open
  Assigned:
• Moving keytar to devDependency
  Status: Complete
  Assigned: @tucker01
• Document how to use plaintext and the default to cli implementers
  Status: Open
  Assigned:
• Use the Managed by instead of securely_stored specified in Make Keytar optional for CLIs imperative#28
  Status: Complete
  Assigned: @lyzla01
• Default to plain text if credential manager is null and Keytar is not "present"
  Status: Complete
  Assigned: @tucker01
• Profiles no longer readable by everyone
  Status: Discontinued
  Assigned:
• Create integration test scenarios for imperative
  Status: In-Progress
  Assigned: @tucker01, @lyzla01
• Create integration tests for imperative
  Status: In-Progress
  Assigned: @tucker01, @lyzla01
• Test changes in a sample CLI
  Status: Complete
  Assigned: @ChrisBoehmCA
• Create sample keytar plugin
  Status: In Progress
  Assigned: @ChrisBoehmCA
• Remove prereqs from CA Brightside CE and Zowe CLI doc
  Status: Complete
  Assigned: @BrandonJenkins14
• Adding text to imperative wiki? (on hold)
  Status: Open
  Assigned:
• General doc review of all content
  Status: Open
  Assigned:
  Parent of Make Keytar optional for CLIs imperative#28