Introduced property $current_page in class Page
- Also added functionality to set <ul> and <li> css classes for pages_list()
- In pages_list() the <li> of the current page now gets class='active' by default
accidentally changed an update
refactored recently added navigaton feature (setting id and class tags)
- html output is now clean, depending on which parameters are set
  * this means, there's no more class="" in any tag
- reafactored code to be wordpress php coding standard conform
fixed some spaces in code => replaced them with tabs
removed 2 more space-"tabs" and replaced them with tabs
fixed issue in copied comment
Fixing conflicts