Add better auth support

[bourdakos1]

This PR brings a few enhancements to authentication:

• The demo panel now allows you to choose the security scheme from a dropdown that is populated by the OpenAPI definition (only showing the dropdown if more than one is listed)
• Adds support for using multiple auth modes simultaneously (Eg: (BearerAuth) OR (ApiKeyAuth AND BasicAuth))
• Adds an authPersistence option to themeConfig.api. Defaults to "localStorage", can be set to false to disable or sessionStorage to only persist while the window is open.

Fixes: #67

[bourdakos1]

FYI @afterthought I think this adds one of the features you were interested in working on:

An option to persist credentials (local storage) to make interactive API exploration a little more user friendly