LUDOC-243 style: Improve formatting of version tags (html)

LUDOC-243 style: Improve formatting of version tags (html)

Improved the xsl templates and the manual.css stylesheet so that the
Lustre version tags would not overlap the text.

- Created a versionbox div class for the div which puts a box around
  version-specific content.
- Created a versioncontent span class for the actual content.
- Put the xsl:apply-templates element inside of a versioncontent span.
- Gave the versioncontent class a margin-left of 15px to move the text
  to the right of the versionlabel.
- Capitalized "Introduced" in the version labels.

Signed-off-by: Ryan Haasken <haasken@cray.com>
Change-Id: I4dbacc082211116626298caf8629e942803725e0
Reviewed-on: http://review.whamcloud.com/10707
Tested-by: Jenkins
Reviewed-by: Richard Henwood <richard.henwood@intel.com>