Changes to satisfy CRAN requests

[mihaiconstantin]

This PR contains changes to satisfy the requests from CRAN. See below:

You still have \dontrun{} examples in:
AsyncBackend.Rd; make_logo.Rd; ProgressDecorator.Rd
Is this really necessary? If not please change them to \donttest{} or
let us know why you think that \dontrun{} is actually the right choice here.

Please make sure that you do not change the user's options, par or
working directory. If you really have to do so within functions, please
ensure with an *immediate* call of on.exit() that the settings are reset
when the function is exited.
e.g.:
...
old <- options() # code line i
on.exit(options(old)) # code line i+1
...
options(...) # somewhere after
...
e.g.: -> R/exports.r
If you're not familiar with the function, please check ?on.exit. This
function makes it possible to restore options before exiting a function
even if the function breaks. Therefore it needs to be called immediately
after the option change within a function.

Please fix and resubmit.