This patch adds support for Office URI Schemes (see
https://msdn.microsoft.com/en-us/library/dn906146).
This will enable browser (non-CMIS) integration of LibreOffice
with MS SharePoint server (v.2013 tested).

In this patch, in addition to ms-* schemes, a new scheme is
introduced: vnd.libreoffice.command, which is analogous to ms-*.
Its purpose is to enable flexible configuration of server and
client, where some types of documents are declared as handled by
LibreOffice, and other are handled by other software. E.g., ODTs
may have "vnd.libreoffice.command" scheme, while DOCXs could be
"ms-word". Client may register LibreOffice to handle both, or to
handle only "vnd.libreoffice.command" scheme.

Unit test included.

TODO in a later patch: add a mechanism to register LibreOffice
to the schemes with OS.

Change-Id: I1c449a211102036f87163058a4c90a93eb32c948
Reviewed-on: https://gerrit.libreoffice.org/27094Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
Tested-by: Jenkins <ci@libreoffice.org>