System Admin: apply string replacements to specific users

[fvlasie]

I had a need to apply string replacements for a single user.

Summary

• Adds an optional Users field on Add/Edit String Replacement so a replacement can apply to one or more people, or to everyone if left blank.
• Stores selected people as gibbonPersonIDList and loads only global rows plus rows that include the current user.
• Checks whether the new column exists before querying it, so the site keeps working until System Admin → Update is run.

To install

• Run System Admin → Update so gibbonPersonIDList is added.

Tested in production (not the best idea I know but it is a minor change). No gibbons were harmed in the production of this PR!