Bugfix for +/- context nav via Microsoft Edge browsers. Display the c…

[seanaery]

…hild nodes and toggle the icon. Fixes #1009.

[seanaery]

A couple minor bugs were preventing MS Edge from working. Edge was interpreting e.target to be the +/- svg; using e.currentTarget instead consistently finds the link element whose click event listener fired. The content CSS property only works consistently with the ::before and ::after pseudo-elements across-browser, so Edge wasn't toggling the +/-. I also removed the hard-coded + icon from the view, leaving it up to the CSS rule to render, which it now does consistently.

[jkeck]

Thanks for this @seanaery! Sorry this took so long to get 👀 on. Doing some build fixes/ rails compatibility updates and wanted to make sure this got in too.