Adding sourcedialog to the plugin builder

I would like HTML edit mode for articles. I'm currently editing by inspecting HTML and changing the content editable element, but that's getting fairly annoying.

Since we use the inline editor mode, the way to do this is actually the "sourcedialog" plugin, not "sourcearea", so I've added that plugin and re-built.

I'm not sure if all the differences in this PR are expected, as this is the first time I've built.

Test Plan:
Add Sourcedialog to toolbar and extraPlugins='sourcedialog' to config, see Source show up on toolbar in article editor.