Bug 12721 - Syspref StatisticsFields: Warning on About page and text change in System...

Bug 12721 - Syspref StatisticsFields: Warning on About page and text change in System preferences

This patch adds a warning to the about page if the syspref 'StatisticsFields' is misconfigured.
Additionally, the text on Home > Administration > SystemPreferences for 'Statistics Fields'
is changed.

To test:
- Apply patch
- Edit syspref 'StatisticsFields'. Verify that the explanation makes sense.
- Leave field empty
  => verify that no message appears on About page, tab System information
- Insert valid field names, e.g. location|itype
  => verify that no message appears on the About page
- Add trailing char
  => verify that the warning message appears on the About page
- Fill in some garbage or misspell a field name
  => verify that the warning message appears on the About page

Signed-off-by: Aleisha <aleishaamohia@hotmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>
(cherry picked from commit 95f492b4d2505103269b295a34bab74804df9746)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>