v0.4.0

• created API wrapper functions for programmatically managing users, apps, user invites,
  roles, etc. See the new API Wrappers vignette for details (vignette("api_wrappers", package = "polished")).
• added 93 new tests for the above mentioned new API wrapper functions.
• removed api_url argument from global_sessions_config(). This argument is only used
  internally during development, so there is no reason to expose it to package users.
• Bug Fix: fixed check for user already registered during sign in process.
• added button_color argument to sign_in_ui_default().
• added tlmgr argument to deploy_app() which allows support for generating pdf documents from
  Rmarkdown.