Consolidate link handling code

[peterflynn]

We have 4 different places that call NativeApp.openURLInDefaultBrowser() after clicking a link tag. Two of them store the URL in "href" and two of them store it in "data-*" attributes. We should make these consistent and use one central piece of handler code.

We should also consider a global capture listener to ensure that we always call preventDefault() for clicks on all links. If someone accidentally left an unhandled link in the UI, clicking it would otherwise navigate CEF away from the Brackets UI, losing all the user's unsaved work.

[pthiess]

Reviewed @peterflynn - bumped it to a medium priority.

[jasonsanjose]

FBNC @peterflynn

[peterflynn]

Confirmed -- code looks all good to me.