sw HTML export: avoid loosing embedded objects when skipping images

(cherry picked from commit 971ffe10583dcdd195f429816760bc0acfb6297f)

Also squash in 3 fixes on top of that:

1) HTML export: avoid invalid output for embedded spreadsheets

When the sc document is embedded inside an sw one, then the sc HTML
export should just write what's inside the <body>. Add a filter option
for that in sc and use it from sw.

(cherry picked from commit 1ee98159f7749b2c1ad47de60a9b3057b9e9720e)

2) sw HTML export: avoid <table> directly inside <p>

Wrapping the embedded object output in a <span> at least makes the
parser errors go away.

(cherry picked from commit 58fc5c6a5153b68470f7de8229b76dca04267ab7)

3) CppunitTest_sw_htmlexport: tinderbox says scfilt dependency is missing

(cherry picked from commit 9f482b596195a2948a8f7f14664a7a870d348e95)

Change-Id: I308e411e4abb938fe08b47aaf21d6fd747bb758e
Reviewed-on: https://gerrit.libreoffice.org/11148
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>