move 'Email' option to Share dropdown on item detail page

[ebenenglish]

When I am on the item detail page (catalog#show)
Under the Tools section
When I click on the Share button
There should be an "Email" option with an envelope icon
And when I click the "Email" link
A modal popup should appear
And the title of the modal should be "Email a Link to This Item"
And when I enter an email address and click "Send"
The popup should disappear

After the implementation of the item-level feedback form, users have reported that having links for "Question/Comment" and "Email" is confusing.

We should move the Email link into the Share options to reduce confusion

To implement this:

• in lib/commonwealth-vlr-engine/controller_override.rb, move the blacklight_config.show.document_actions.delete(:email) line from line 259 to a new line below 211
• add the Email link (currently rendered by app/views/catalog/_show_email_tools.html.erb) into the Share link list (app/views/catalog/_sharing.html.erb)
• add a comment to app/views/catalog/_show_email_tools.html.erb indicating that the link has been moved, but we will keep this file in case we need it later

[ebenenglish]

Fixed via #132