Renormalize indentation whitespace to tabs

[stakx]

This fixes #364.

[JohanLarsson]

FWIW I prefer four spaces, renders nicer when reading code in the browser if nothing else.

[stakx]

Yes, I personally prefer four spaces, too. They have the additional advantage that multi-line (wrapped) statements can be properly indented without running into the question of whether & how to mix tabs and spaces.

For now, in this commit, I did not want to let my personal preferences intrude: I decided to adhere to .editorconfig and to what the majority of Moq's lines of code already use. That doesn't mean that we can't change everything to spaces at a later point in time. At least for now, we have some consistency again.