Mark \shp and \shpinst as supported control words on rtf reader

Summary:
The destination don't get specific handling at the moment, but might
contain images etc. Suppose it's lesser bad to show them even without
all the properties read than to omit them.

Some other control words are in similar way marked as supported but
without destination handler class.

Reviewers: denexter, davidllewellynjones

Reviewed By: denexter

Subscribers: Calligra-Devel-list

Tags: #calligra:_3.0

Differential Revision: https://phabricator.kde.org/D25285