[TASK] Implement own method building default view configuration for ext key

Implement an own method building the default view configuration of the
given extension key, so it can be better extended by sub-services like
fluidpages or fluidcontent, which can provide by default a deeper folder
structure. (e.g "Templates/Page" for fluidpages or "Templates/Content"
for fluidcontent).
[TASK] Make method building the default viewconfiguration protected
Merge pull request #599 from higidi/feature/implement-own-method-for-building-default-viewconfiguration

[TASK] Implement own method building default view configuration for ext key