Remove trailing slash from publishing endpoint specified in user settings

[hmaier-fws]

Issue

Refactor user specified "Publishing Endpoint", defined on "Settings" screen to not require a trailing slash.

Issue Description:

Currently, the mdEditor throws an error if the "Publishing Endpoint" specified by the user, does not contain a trailing slash. Other user specified settings (e.g., "Import URL", "mdTranslator API URL") entered by the user do not require a trailing slash.

The change will provide a consistent method for users to enter default values.

Updates to be made:

• Refactor ScienceBase publishing code to append a path separator after the value provided by the user in the "Publishing Endpoint" setting
• Update CONTRIBUTING.md - no trailing slash for user specified settings #752