Implement inherit from module feature for mods data
The basis for inheritance should be specified for each mod as the property "inherit" of exports.BattleScripts in scripts.js files.
This intends to fix the current data for old generations, so that they inherit from Gen5, as originally.
(Per kotarou3's and Zarel's requests in #444 and #451.)
Specify the basis for inheritance of every mod needing it
Create scripts.js file for gen5bw in order to do so.