Pimpl-ed, renamed and exported ImportMetadataWidget to DvcsImportMetadataWidget

ImportMetadataWidget is pimpl-ed, renamed to DvcsImportMetadataWidget and exported for (near) future use in new VCS plugin.

REVIEW: 118460

From 8070a78a6be7d5eab06a0b701520ef950793512d Mon Sep 17 00:00:00 2001
From: Maciej Poleski <d82ks8djf82msd83hf8sc02lqb5gh5@gmail.com>
Date: Sun, 1 Jun 2014 23:59:06 +0200
Subject: [PATCH 1/1] Pimpl-ed, renamed and exported ImportMetadataWidget to
 DvcsImportMetadataWidget