$SessionID already contains a semicolon.
Remove <base> tag from HTML in articles.

Fixes bug#8880 - No inline image shown if HTML email contains 'base' tag
http://bugs.otrs.org/show_bug.cgi?id=8880

The <base> attribute breaks any <img> tags pointing to relative sources.
This is the case in some mails generated by MS Outlook. In that case
the inline images do not show.
Removed duplicate semicolons from tests.
Fixed typo.
Fixed generation of random ID in sender string.
Merge remote-tracking branch 'upstream/master'