Allow the vat rate to be specified to two decimal places

Allow values like 19.75 to be entered.

Set the step increment to 0.1 and the page increment to 1.0.

Signed-off-by: Andrew Clayton <andrew@digital-domain.net>
Tidy up the help window

Create the help window at a reasonable initial size, but allow it to be
resized.

By setting the GTK_WRAP_WORD property of the text view we can get rid of
all the \n's that were used to break up the lines in the paragraphs.

Now the help text will be flowed properly as the window size is changed.

Signed-off-by: Andrew Clayton <andrew@digital-domain.net>
Add an icon

Time for it to have its own icon.

The icon is made up from

http://openclipart.org/detail/167894/barrel-rendered-by-kevie
http://openclipart.org/detail/166696/nuclear-explosion-by-tzunghaor

and was put together by Graham Thomson <graham.thomson@gmail.com>

Signed-off-by: Andrew Clayton <andrew@digital-domain.net>
vatmageddon 009

Signed-off-by: Andrew Clayton <andrew@digital-domain.net>