Removed chained string from label. Fixes #11

Chaining `$label .' '. __('Page', 'display-widgets')` potentially can
create issues in other languages than English. In German, for example,
there is no way to chain translations for `$label` (like for `Single
Post`) with a following `Page`. A translatable string should always
contain complete message in order to enable translators to translate in
context.
Updated German localization.
Merge pull request #12 from glueckpress/display-widgets-de_DE

Localization de_DE
Thank you @glueckpress!