Add a button to link sentences by id
Fix #447 while we’re at it.
Simplified rendering using a separate template.
Fix HTML edition from JS.

We were inserting the new div inside the old div, but we want to replace
the old with the new instead.
Clean error reporting using ajax linking.
Allow to enter a sentence link in the ID field.
Be consistent with other ajax things.

• Add a loading icon
• Don’t remove the field contents until the operation completes
Support linking sentences by drag and drop.
Prevent CakePHP from barking.

This will eventually allow us to print a more precise error message
about why the link insertion failed.
Allow form submission using enter key.
Fix link button for sentences added through ajax.
Refresh all translations when linking/unlinking with the icon next to translation
Fixed padding so that opening the link input doesn't add an extra line
Display loading icon in sentence menu instead of translation group
Merge pull request #484 from Tatoeba/link-to-any

Add a button to link sentences by id