* moving commonly used strings to defines
* moving commonly reused/similar page generation functions to the parent
* generally using consistent return types, more type hints and less strings
* prevent browser context menu when right clicking on UI elements with their own context menus
* fixed menu path for icons
* be a lot more verbose when errors are occuring (to staff anyway)
* made hardcoded error messages for comments localizable
* add error messages from posting comments to session to be displayed on next page update
* access class property in screenshot/comment-admin by function. Aowow is compatible with PHP 5.5 again
* changed line-endings across the board from \r\n to \n
* separated into appropriate subclasses
* unified sanitizing of $_GET and $_POST data using build in filter_input()
* index now always tries to resolve page calls with ajaxHandler first and as a page last
minor bug-fixes to bugs that wre not reported yet, because they didn't occur yet
(e.g.: nobody tried to compose a comment with >7500 characters yet)