Removes System.Drawing from IdSharp.Tagging

[atruskie]

Hi!

Please excuse the direct PR but I figured it was easier to submit a patch with the work done (and to change it if necessary) rather than explain this in an issue.

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When installing this library via nuget, it also attempt to install System.Drawing (and System.Win32.Events):

Coupling this library with System.Drawing for one use case is unnecessary, especially when many libraries have gone to great pains to remove System.Drawing form their stacks.

This commit moves the System.Drawing parts of AttachedPicture into a separate project so that those references do not pollute the main library.

More work is needed to, especially in deciding whether or not to keep the AttachedPictureWithImage class and possibly publishing a new nuget package as well.

What do you think?