Feature/clipboard place holders

[bassmanitram]

Adding placeholders that insert the textual content of the clipboard.

Courtesy of @supermerill.

This adds two new placeholders to the extension:

• %v to insert the XA_PRIMARY selection content (think middle mouse button after selecting text)
• %V to insert the XA_CLIPBOARD selection content (think CTRL-V of CTRL-C'd text)

(For more info on the X selection categories, see the manual pages for clipboard management programs such as xclipboard, xclip, xsel, xcutsel ...)

If the selected text contains quotes, parameter quoting may be corrupted, so these should be used carefully.

Hopefully, we'll address parameter quoting in general in a future PR to alleviate these issues.

[bassmanitram]

Hey there @supermerill

So this is what I've come up with - I'd really appreciate you testing this to see if it fulfills the use cases you had in mind.

I'm sure you know what to do, but just in case:

• Sync your repo with this repo
• Checkout the feature/clipboard-place-holder branch
• Reinstall the extension
• Kill Nautilus (nautilus -q)
• Fire it up again and test.
• Let me know how it goes

If you have further PRs for this feature, please submit against this branch, not master.

And thx again for this excellent idea and the initial implementation!