Fix deprecation errors in the console

Problem/Motivation

Looks like a few configuration options are deprecation in the global configuration:

[Warning] [SkipTo]: Unsupported or deprecated configuration option in global configuration object: buttonLabel (skipto.min.js, line 18)
[Warning] [SkipTo]: Unsupported or deprecated configuration option in global configuration object: smallButtonLabel (skipto.min.js, line 18)
[Warning] [SkipTo]: Unsupported or deprecated configuration option in global configuration object: altLabel (skipto.min.js, line 18)
[Warning] [SkipTo]: Unsupported or deprecated configuration option in global configuration object: optionLabel (skipto.min.js, line 18)
[Warning] [SkipTo]: Unsupported or deprecated configuration option in global configuration object: shortcutLabel (skipto.min.js, line 18)

see https://skipto-landmarks-headings.github.io/page-script-5/config.html

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes