Add LGPL licence for library directory

We've received some requests to create a way to interface with crtools
that doesn't involve forking the utilities, so we're going to create a
linkable library for this.  In order to be fair, we plan to allow
proprietary code to link with this library and thus want to change the
licence of the CRIU code base to be LGPL *only* for this library
directory, preserving the rest of the code as GPL.  Because creating the
library may involve refactoring, I anticipate that some code that's
currently GPL will have to move into lib/ and become LGPL (and this may
occur in future as well), so I've amended the COPYING file to spell out
for contributors that code outside lib/ is GPL and inside lib/ is LGPL,
but that they give future permission to change the licence to GPL or
LGPL if code has to move into (or out of) lib/, based on acceptance of a
patch into the CRIU code base, so j random developer can't download the
code and make it all LGPL by applying a private patch to move everything
into lib/.

All the Parallels authors have agreed to this, but we have a couple of
non parallels ones on the cc to this email I'd like explicit acks from.

Cc: Qiang Huang <h.huangqiang@huawei.com>
Cc: Andrew Grigorev <andrew@ei-grad.ru>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
Acked-by: Qiang Huang <h.huangqiang@huawei.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>