Fix EZP-23126: do not redirect to /login when in legacy_mode
[Test] Change back to mock interface

Should be fixed now in hhvm-nightly as of:
https://github.com/facebook/hhvm/commit/8ecf23470b640067ae9daffbaa38f02828ae3996

So changing this back to how it was.
[SPI] Change ContentHandler->load \$translations to be array

It is documented and used as an array if not null, so make this enfoced
so we don't need to check all over.
Merge pull request #918 from joaoinacio/EZP-23126_legacymode_login

Fix EZP-23126: do not redirect to /login when in legacy_mode
Merge pull request #920 from ezsystems/hhvm_interface_test

[Test] Change back to mock interface
Implement EZP-23134: Cache content load calls with translations

Since Stash is hierarchical, add a extra layer for translation string.
Merge pull request #921 from ezsystems/spi_cache_content_load_w_translations

EZP-23134: Cache content load calls with translations
Fix EZP-23074: Missing form token meta tags when browsing legacy modules

https://jira.ez.no/browse/EZP-23074

Alternative of https://github.com/ezsystems/ezpublish-legacy/pull/1026

This acts with a Response listener, triggering `ezxFormToken` output filtering once again,
to ensure meta tags containing CSRF token are present.

Note that `ezxFormToken::output()` has been slightly modified as well.

## About cache
There is nothing to worry about here since HTTP cache is assumed to be handled by legacy modules.
**`LegacyKernelController` does not set cache headers on its own**.

See [`LegacyResponseManager::mapHeaders()`](https://github.com/ezsystems/ezpublish-kernel/blob/master/eZ%2FBundle%2FEzPublishLegacyBundle%2FLegacyResponse%2FLegacyResponseManager.php#L141) for more insight.