Refactor fetching versions

- Procedural code moved to OOP
- Added unit tests
- Added a more flexible tmp folder location and introduce var folder
(in production this won't work

Refactor fetching versions

- Procedural code moved to OOP
- Added unit tests
- Added a more flexible tmp folder location and introduce var folder
(in production this won't work yet, so we still use /tmp there).
For local development environments var directory in project root
is used for faster and easier project setup.
- Added initial extensible PSR-16-alike semi-compatible cache class
and refactored storing fetched versions.
- The versions list generator is now simpler and a bit more logical
what is happening. Versions sort order is the same as before.
- Added ComposerScripts utility/service class for creating required
directories (uploads and var/cache), and configuration file, when
installing application in development environment.

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