Expand the commenting tools to get them on par with the ones in the desktop version.

In particular, the desktop version has the option to strike-out, replace and add text. The online/browser version only allows to strike-out text. Though one can add also "comments" to the strike-out markup, however, this would also require to manually change the color to blue which is the default for replace or added text in the desktop version.

Also, in the desktop version one can simply select a word by double-clicking and start typing to "replace" the work or passage with new text. This is an extremely handy feature when proof-reading PDFs and seemingly trivial to implement also in the browser/online version.