bnc#862510: PPTX import: bullets have color as following text by default.

aTextCharacterStyle contains font theme color set in Shape::createAndInsert.

Change-Id: I55e66aeaa7176fbd3f64dcdf075d411f460947d4
(cherry picked from commit d60cec0e60c5c0880f8098d39443c391abed80b2)
Reviewed-on: https://gerrit.libreoffice.org/10516
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>