In a PR we have to keep an eye on a lot of different things. But sometimes the
bare code is the key-thing we want to care about and just don't want to care
about fixed indention on some places. Especially if we follow the pathfinder
rule we face a lot of these situations because these changes don't break the
code in many languages but improve the readability a lot.

So this change introduce a fine graned button to adjust the way how the
reviewer want to see whitespace-changes within the code.

The possibilities reflect the possibilities from git itself except of the
`--ignore-blank-lines` flag because that one is also handled by `-b` and is
really rare.

Signed-off-by: Felix Nehrke <felix@nehrke.info>