oox, writerfilter: Support for artistic effects on pictures

Bitmaps can define artistic effects like in the following example:

  <a:blip r:embed="rId5">
    <a:extLst>
      <a:ext uri="{BEBA8EAE-BF5A-486C-A8C5-ECC9F3942E4B}">
        <a14:imgProps
         xmlns:a14="http://schemas.microsoft.com/office/drawing/2010/main">
          <a14:imgLayer r:embed="rId6">
            <a14:imgEffect>
              <a14:artisticMarker trans="14000" size="80" />
            </a14:imgEffect>
          </a14:imgLayer>
        </a14:imgProps>
      </a:ext>
    </a:extLst>
  </a:blip>

They are defined in the MS-ODRAWXML extension. Ref:
http://msdn.microsoft.com/en-us/library/dd905216(v=office.12).aspx

LO core doesn't support them, but I'm preserving them using the shape
grab bag. Bitmaps must not be transformed to a SwXTextGraphicObject
so the grab bag of the XShape is not discarded.

Added several Context and Properties objects on the import side to
traverse and save the relevant tags, and added the corresponding code
on the export side to extract the grab bag and output the effect back.

When Word applies an artistic effect, it creates two embedded files;
one contains the bitmap with the effect and the other one contains the
original bitmap to be able to undo the effect. We also read the
original bitmap, store it in the shape grab bag and save it back to
the docx file.

When two pictures apply different effects to the same picture, it is
only saved once in the original document. Added a cache to DrawingML
to know if the picture has already been exported.

Finally, added unit tests for a selection of artistic effects.

[Squashing commits from master:
  21d4cfe19e2796ebf89c408e292c4473924b2bc4
  642a252cf1a2f1d08c4bbfcae15527bb82c7664d
  2e68a1468c035fc3bb4d02ad0b3187872fe1e67b
  b5f6a5cfc517ecd8aa6ba96471d854b07b92ebaa
  38d7b82c277599f2e613256c4353aa7dfdc219ec]

Change-Id: I39327a8118e23829c029122154a31ce3af5b48cd
Reviewed-on: https://gerrit.libreoffice.org/9495
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>
Updated core
Project: help  0040595dcb207b21f81349af1b71fcd854f3b589

fdo#79530 Update help for minimum length of password

Since some time, password only required 1 character (as indicated in UI)
instead of 5 as indicated in help

Change-Id: Id7fef69ee273ee622365b4077d83cd46368475c6
Reviewed-on: https://gerrit.libreoffice.org/9624
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>
(cherry picked from commit 99e6e19c88313251a236ef25150d339b930c7f9a)
Reviewed-on: https://gerrit.libreoffice.org/9630