[TASK] Respect global settings for timestamps in asset filenames
[FEATURE] Add PDF thumbnail viewhelper
[TASK] Add "pdf" prefix to generated PDF thumbnails

This adds a dead-simple pdf prefix to the generated filename.
That way, one is able to simply delete all vhs-pdf-* files
from typo3temp without much hassle after fiddeling with ImageMagick
[TASK] Add the ability to modify the class of the current language

A sensible default was provided to not break older versions.
[BUGFIX] Languages argument can be left empty

In that case, the v:page.language ViewHelper will simply return the current languages uid.
[BUGFIX] Correct order of included assets
[BUGFIX] LinkViewHelper should respect tag-content in translations

This fix postpones the title setting for sys_language_uid to the latest possible
point to overcome a bug.
Otherwise, the tag content wouldn't be taken into account when sys_language_uid != 0
[FEATURE] Rootline view helper
[TASK] First draft for a more tight integration to Travis