v.7.26.1

Changelog:

• Feature: 'Migrate MathType plugins suite from TravisCI to Github Actions'.
• Fixed 'Plugin not loading when Moodle install folder is different from the root' (KB-13266).
• Bump 'MathType for TinyMCE4' to 7.26.2 (KB-13266).

Fixed 'Moodle install folder is not root'

Update MathType for TinyMCE4' to v.7.26.2 that includes a fix for the Moodle Integration.

This change fixes #57.

Migrate test build machine from TravisCI to Github

• Update CHANGELOG
• Fix lint issues on privacy class.
• Add workflow based on 'moodle-plugin-ci'.
• Remove TravisCI script from the project.
• Update .gitignore with custom paths.
• Update CHANGELOG
• Add full matrix to the tests
• Fix third-party vulnerabilities