Allow and use a text.dat.local override file

The wiki suggests 4 methods to overwrite text.dat entries, all require the sysop to alter either text.dat or adding lines to existing files, therefore necessitating the creation of /sbbs/mods version. Once this is done, it's more difficult to maintain updates scripts.

Allow the sysop to create /sbbs/ctrl/text.dat.local or /sbbs/mods/text.dat.local that only includes overwrites for existing entries. This file can then be read when require("text.js"... is used and would require the user to do nothing more than add text to text.dat.local.