Fix for Bug 6884, Improve TinyMCE configuration on Koha News page

Fix for Bug 6884, Improve TinyMCE configuration on Koha News page

- Increases the width of the editor to fill the space provided
- Adjusts the layout of the toolbars to better fit the space
- Adds a custom editor stylesheet to make the contents of the
  editor better match the expected output

In changing the toolbar configuration I chose to make the display
of each button explicit rather than assuming a default set of
buttons and adding or subtracting from that. I think this is
clearer for someone approaching the configuration trying to under-
stand how buttons are displayed. I also chose to use the
shorthand "|" instead of "separator" for brevity. This last change
is the only one made to the edithelp configuration.

[2011.09.20] F. Demians. This patch is compatible with bug 6649 patch,
fixing help pages editing, and so could be applied before or after it.

Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
Signed-off-by: Ian Walls <ian.walls@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>