Implemented scrollbar buttons left, right, up, down

input_hscrollbar_leftbutton, input_hscrollbar_rightbutton,
input_vscrollbar_topbutton, input_vscrollbar_bottombutton
Implemented input_hscrollbar_left_trough
Some consistency cleanup
Implemented input_hscrollbar_right_trough
Implemented input_vscrollbar_top_trough
Implemented input_vscrollbar_bottom_trough
Formatting
Merge pull request #204 from AngeloG/scrollbar-buttons

Implemented scrollbar buttons left, right, up, down