Speed up, multi buy & sell, encumbrance

* Converted var declarations to use let and const where possible.
* Tried to enhance speed of algorithms.
* Added selection of multiple items to pick, put, buy or sell with traders and containers.
* Used new hyperlink RPGM template syntax to add hyperlinks to select all of a type of item, or all items in the container.
* Added encumbrance.
* Updated attrLookup() and resolveData() to use objects for optional parameters.
* Fixed viewing spell storing MIs in inanimate containers.