Provide editable AcroForms support in PDFViewer.
The current implementation of the Kendo PDFViewer depends on pdf.js, so the following should be taken into account:
1. Allow the elastic behavior of the PDFViewer's mobile scroller to be disabled. Currently, when scrolling to the top or to the bottom, the document jumps and then immediately re-adjusts its position under the widget's header/bottom border.
2. Add the ability to manually scroll the document up/down with mousedown.
3. Add keyboard scrolling support.