* GH-708/709/634 Improve eslint config & update to Theia 1.27

GH-708:
- Refactor eslint config according to the recommendations of https://typescript-eslint.io/docs/linting/monorepo/
Part of https://github.com/eclipse-glsp/glsp/issues/708

GH-709
- Update examples and templates to Theia 1.27 / GLSP 1.0.0-theia1.27
Fixes https://github.com/eclipse-glsp/glsp/issues/709

GH-634:
- Update jenkins config to also build project templates
Fixes https://github.com/eclipse-glsp/glsp/issues/634