Added ability to add sprintf variables to JText string

[writing it up now...]
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Added ability to use custom non-language string as first part (can be used for concatenating other strings)
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Merge remote-tracking branch 'remotes/upstream/master' into patch-9
Merge pull request #880 from nonumber/patch-9

Added ability to add sprintf variables to JText string - Thanks Peter.
 # [#30804] [3.x] *plug-in manager search give errors and warning for
'/','*' and '\
(Fix #1235)
Merge remote-tracking branch 'origin/master'
Changelog + Jversion in installation ini
 # [#31073] Preview image has height of max 18px. Thanks Piotr Konieczny
(Fix #1229)
 # [#29766] Missed ordering lists in User Manager. Thanks Aleksander
Linkov
(Fix #862)
 # [#30675] Display incorrect for type checkboxes. Thanks Chad Windnagle
(Fix #1228)