Refreshing access tokens on demand

[Xemdo]

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Problem/Feature

Adding a feature to refresh access tokens via the CLI.
Resolves #307

Description of Changes:

• Added --refresh flag to twitch token, allowing users to refresh their access tokens.
• Added --secret flag to twitch token, allowing users to override the Client Secret as it currently defaults to the one in the config.
• Moved error handling and messaging for token and login stuffs upstream out of login.go and into callers like token.go

Checklist

• My code follows the Contribution Guide
• I have self-reviewed the changes being requested
• I have made comments on pieces of code that may be difficult to understand for other editors
• I have updated the documentation (if applicable)

[SputNikPlop]

LGTM, like how you the error handling is