Add whitespace ignoring

[glconti]

• [x] change button icon to a nicer one

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This change is 

[laurentkempe]

Having the new button on the contextual menu is confusing because you tend to think that it applies only to this hunk when it applies to the whole file

I think it would be better to have it only on the menu bar

[laurentkempe]

When ignoring whitespace is on and a white space is added at the limit of a hunk, it shows changes which it should not do