Bug 14135: Adds 'Free' to variabletypes in systempreferences.tt

Bug 14135: Adds 'Free' to variabletypes in systempreferences.tt

The 'Local Use' system preference addition/modification template provides the following options against "Variable Type" - Choice, YesNo, Integer, Textarea, Float, Themes, Languages, Upload or ClassSource.

There is no option presented for "Free" which seems to be the most
used variable type out-of-the-box (i.e. INTRAdidyoumean,
OPACdidyoumean, UsageStatsID and UsageStatsLastUpdateTime)

This trivial patch proposes to modify the systempreferences.tt
and add the option 'Free' to the list offered to users.

Test Plan
=========

1/ Go to Home > Administration > System preferences > Local use
2/ Click on 'New preference'.
3/ In the fieldset 'Koha Internal', the variable types offered
   are Choice, YesNo, Integer, Textarea, Float, Themes,
   Languages, Upload or ClassSources.
4/ Clicking on 'Choice' should set the 'preftype' field as
   'Choice'.
5/ Apply this patch.
6/ Refresh the page.
7/ The variable types list should read - "Free, Choice, YesNo,
   Integer, Textarea, Float, Themes, Languages, Upload or
   ClassSources".
8/ Clicking on 'Free' should set the 'preftype' field as 'Free'.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
NOTE: Discovered that there is no validation on the type field.
      However, that is beyond the scope of this bug.

Signed-off-by: Amit Gupta <amit.gupta@informaticsglobal.com>
Signed-off-by: Jonathan Druart <jonathan.druart@koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>