* Switch to symfony/cache; closes #8561

1. Use filesystem by default.
2. Drop support of APCu/Wincache (and so remove footprint file checks).
3. Remove fallback to memory cache when configured cache adapter fails.
4. Handle configuration outside database.
5. Add a configuration command.
6. Remove cache contents from debug tab (weighs too much and not really usefull).
7. Test, test, test !

* Drop couchbase support

* Drop file:// scheme definition

* Add memcached to test suite

* Fix namespace normalization

* Fix tests

* Show memcached version