Created new assets and modified xml to clean up tabbed IM window layout.

indra/newview/skins/default/textures/textures.xml

...kins/default/textures/widgets/ScrollArrow_Left_Opaque.png

...default/textures/widgets/ScrollArrow_Left_Over_Opaque.png

...ins/default/textures/widgets/ScrollArrow_Right_Opaque.png

...efault/textures/widgets/ScrollArrow_Right_Over_Opaque.png

...a/newview/skins/default/textures/widgets/jump_left_in.png

.../newview/skins/default/textures/widgets/jump_left_out.png

.../newview/skins/default/textures/widgets/jump_right_in.png

...newview/skins/default/textures/widgets/jump_right_out.png

indra/newview/skins/default/xui/en/floater_im_container.xml