Added the class "nav-icon-recent" to display the new "recent files" file list view to be added by @icewind1991 in PR #292

It's now placed after nav-icon-files which was where @jancborchardt was suggesting iirc.

Add the new icon for "Recent files" file list view in the files app by @icewind1991, as discussed in PR #292

Icon is already compressed/cleaned by scour rather than svgo as svgo seems to corrupt it.

Change colour of the "recently used files" icon from grey to black, to match other icons in the files app.

Just updates the colour of the icon for "Recent files" from a grey version, to a black optimised version.