feat(openPlunkr): enable ctrl+click

[ghoti143]

This is an initial suggestion for dealing with the problem described in #10641. To summarize, the problem is:

• The "Edit in Plunkr" anchor tag has an ng-click attribute
• The openPlunkr function is fired on click which calls formPostData
• formPostData creates a new form element, adds it to the page, posts it, and removes the form element
• The form, when posted, opens in the same page (target="_self")
• This can be unhelpful for people who want to stay on the AngularJS documentation site.
• Changing the target attribute to "_blank", however, can trigger the popup blocker.
• If a user chose to bypass pop-up blocker one time and click the link, they would arrive at a new default plnkr, not a plnkr with the desired template.

To resolve, the following steps were taken:

• Pass the $event object into the openPlunkr function
• Check if the ctrl button was pressed during click
  • If true, set target="_blank"
  • If false, set target="_self"

This enables a user to "opt-in" to the new window functionality, and the assumption is that they will whitelist the AngularJS docs page so their popup blocker doesn't block the popup. However, for the users who do not ctrl+click, they will continue experiencing the default functionality and not experience the undesired behavior described above.

[caitp]

it looks good to me, tbh. tries it

[caitp]

added one more commit to it to work better on macs, since by default ctrl+click is right-click