Implementation of DownloadManagerDelegateEfl class

Implementation of DownloadManagerDelegateEfl class

The patch implements DownloadManagerDelegateEfl::DetermineDownloadTarget,
which allows to use Chromium downloads.

We are checking whether the external download manager is available,
in order for it to be considered, before using Chromium fallback
download code.

Right now, PathService class is used to determine where downloads
should be saved on given platform based on mime type.

Original beta/m47 patch:
- http://web.sec.samsung.net/gerrit/#/c/96713/

Bug: http://web.sec.samsung.net/bugzilla/show_bug.cgi?id=14817

Reviewed by: a1.gomes

Change-Id: Ia1362cad11044dab4de4e1ee7eb908ebeee3c995
Signed-off-by: Pawel Niemirski <p.niemirski@samsung.com>
(cherry picked from commit d0bde5a4fdf6f0591bf194478e1b7f3b5997bd00)