EMF+: Parse and render custom line cap data.

Contains the following commits:

* EMF+: Small cleanup & more logging in preparation for line starts & ends.
* EMF+: Parse custom line cap data for start and end line caps.
* EMF+: Render custom line cap data.
* EMF+: Set the stroke attributes on the custom line caps.

Change-Id: If35ef1c44f34f5d5e6c50789c907105d03e96fca
Reviewed-on: https://gerrit.libreoffice.org/6806
Reviewed-by: Andras Timar <andras.timar@collabora.com>
Tested-by: Andras Timar <andras.timar@collabora.com>