Add setting to add trailing commas

[Sebastiano Poggi]

Right now the plugin never appends a trailing comma, but some code styles require it. Would be nice if the plugin provided a setting to add trailing commas.

You probably should use projectConfigurables (see the docs here) to allow per-project settings to differ.

EDIT: nevermind, didn't realise it's an inspection — I suppose you just need an extra checkbox there then :)