Fix Edit bugs, mainly related to spaces.
Trailing spaces were not included to drawn text (so they were
treated as "empty"), because so does CustomLayout example, the logic in
EditLayout came from. But Edit control is editor, not printer, spaces
must be included and therefore logic to exclude trailing spaces is removed.
Fix bug that selection is not relaxed after clicking past-of-the-end area.
Add clipping Edit area.
Add Scrollbar paging timer which makes scrollbars page up/down
periodically during their paging area is clicked.