Fix http_cache of issue 1246

[joeherold]

@leofeyer
@Toflar

This pull-request should fix the issue, with the not working http_cache.

Tested in my local environment and works like a charm.

The implementation also preserves the ability, to cache inserttags individually and do not cache insert tags with the pipe uncached or refresh.

This should fix the problem from issue http_cache not working #1246
(#1246)

A new event listener (FinalCacheHeadersListener) is restoring the cache headers.

[leofeyer]

This is basically the same approach as #1283, which we have decided against.

[joeherold]

@leofeyer great, @Toflar asked me to do so...
#1246 (comment)

Yeah we might need to do so. But also I would like to make this dependent on the global $objPage, so essentially moving the FrontendTemplate::setCacheHeaders() into that listener. Would you like to work on a Pull Request for the Core-Bundle for that? That would be awesome

[leofeyer]

@joeherold We have a core developer's meeting next week and this topic is on our agenda. Is it ok if we delay this discussion until after the meeting?

[joeherold]

Sure. To not have stress I made the 3rd Party Bundle as a quick fix workaround. https://packagist.org/packages/pliigo/pagecacheenabler-bundle.

So anyone needs it now, can help himself by installing it via manager.

I just made it, because yannick asked to. feel free to discuss.

[Toflar]

I didn't know about the solution in #1283 (which indeed is the same), sorry. It's impossible to keep track of all the stuff that's going on :S

[joeherold]

@Toflar Auf den Kaffee od. Bier freue ich mich dennoch :)

[leofeyer]

See #1388 now.