Hunk header does not interfere with line wrapping

[jensenr30]

The Hunk Header was interfering with line wrapping. This video shows how the Hunk Header causes the line wrapping to stop working:

gittyup-line-wrap-header-1-no-wrap.webm

This PR fixes this issue by making the hunk header resize itself according to the size of the DiffView windows:

gittyup-line-wrap-header-2-wrap.webm

Also, the DiffView still has line wrapping disabled by default. When line wrapping is disabled, the new Hunk Header still works as expected:

gittyup-line-wreap-header-3-no-line-wrap.webm

[Murmele]

I have to check why the appdata check does not work anymore.
I created an issue I have to checkout the linux build problem: #722