Move patch command out of VcsPlugin

It will be needed soon inside DiffEditor plugin.
Move "Patch command" setting out of Version Control | General
into Environment | General | System.

Introduce PatchTool class, which hold the patch command
setting and a method for applying patches (runPatch() - moved
from VcsBasePlugin).

Change-Id: I9de94358ccd5c6e31ac2beefc27305c5111d67bb
Reviewed-by: Jarek Kobus <jaroslaw.kobus@digia.com>