[Visitors] Version 3.5.1 RC1

A new version is online, 3.5.1-RC1, for testing. (for composer and in ER2)
The following points have been adjusted:

• Fixed #105, language variable for "startdate not defined" was wrong
• Fixed #107, Statistics Select form is shown wrong on MAC
• Fixed #183, Statistics button in the category overview, target category was ignored
• Feature #102, In Reader Sites (News / FAQ) count the articles as a page.
• Feature #96, Access protection for the statistic
• Feature #85, Adjust visitor statistics for the flexible BE-Theme
• Feature #106, new language files: Hindi
• Feature #106, new language files: Russian
• Analyze code with help of SensioLabsInsight, fixed many hints