Doc - Don't use ditaa anymore

[Simran-B]

It gives you very little control over the style. Creating an equivalent image with GIMP, Inkscape or whatever is more or less the same in effort. ASCII art is nice, but we never really used it.

[Simran-B]

May fail on checkout because the oskar script does not seem to cover the case of untracked files causing a conflict:
https://github.com/arangodb/oskar/blob/master/scripts/switchBranches.fish

Throwing away local changes by git checkout -- doesn't cut it, because this won't affect untracked files. git reset --hard and git clean -fdx seem to be carried out only if and git checkout "$branch" was successful and clean is set to true. In the else branch, nothing removes untracked files.

A possible solution would be to git checkout --force $branch, perhaps only if clean is set to true.

[Simran-B]

Moved to arangodb/docs#12