[RFC] Allow empty page titles

[kiler129]

Short description of what this feature will allow to do:
In the original implementation the CrudDto::getCustomPageTitle() returned empty strings when empty strings were set via Crud::setPageTitle($pageName, ''). This behavior changed as a part of #5066 and empty() check was introduced, which later on became an explicit check for an empty string or null.

While this behavior makes sense in terms of null, to provide default values automatically, the empty strings should be allowed in my opinion.

Example of how to use this feature
In my use case some of the lists are embedded in a context where the title is legitimately empty and shouldn't be displayed. Currently it isn't possible to leave the title truly empty without overriding the template, which isn't very flexible. A dirty workaround is to set the title to a single space, which is obviously less than ideal. Setting the title to a false will produce an empty title, but this isn't an intended behavior given the function parameter type.

Scope
I propose to allow empty strings to be considered as valid titles, like in old versions. This makes the intent clear:

• null = "I don't have an explicit title" vs.
• '' = "The title is known to be an empty string".

This may constitute a small BC break unfortunately. I don't think introducing any more complexity for this is worth it, unless someone has a better idea. cc @Lustmored as the empty() behavior change looks unintentional as part of the PR.

WDYT?

[Lustmored]

I think the problem comes from the fact that internally EA is currently using Translatable objects to store translatable content and therefore passing an empty string would produce a TranslatableMessage object with empty string, so that it's not and empty value anymore. It'd get weird during translation, but could work for sure.

Alternatively you can pass a TranslatableMessage object with an empty string as a value (Crud::setPageTitle($pageName, t(''))) and you will probably get what you need. But I'm not sure, you'd have to experiment with that.