Preserve <span> information in MultiText strings

This fixes http://jira.palaso.org/issues/browse/WS-34799, at least
to a first approximation.  No attempt is made to keep the spans in
sync with any editing of the field.  The user is not shown anything
to indicate that spans exist underneath to affect the formatting.
Merge pull request #59 from sillsdev/Fix-WS-34799

Preserve <span> information in MultiText strings