[Fixes bug #1064018] Data lost when pasting images onto smaller canvases

[don-mccomb]

Modified code in the PasteAction to create a selection layer of the same size as the image data on the clipboard.

Copied a lot of the code from the PasteAction to the PasteIntoNewLayerAction. Modified this code to create and work on a new layer.

[cameronwhite]

Thanks for the pull request!

With these changes, there isn't much of a difference between the code for Paste and Paste Into New Layer anymore. I think it would be good to eliminate the duplicated code and just have a common function that handles the pasting (and has a boolean argument for whether to create a new layer).

[don-mccomb]

I agree. Will see what I can do tonight.

[don-mccomb]

I've replaced the majority of the code in the Activated method of the PasteIntoNewLayerAction class with code to activate the AddNewLayer and Paste actions. Much cleaner. The only downside is that it creates 2 separate entries in the History: one for the AddNewLayer action and another for the Paste action.

[don-mccomb]

While I like the cleanness of the code in my last commit, the user experience is subpar. The user should not have to undo twice to undo the PasteIntoNewLayerAction. Will modify...

[cameronwhite]

Just have the one comment above, but it looks good otherwise.