Improve Custom item creation and handling

[Andre601]

Description

This is a rather large PR as it changes and improves a lot of things for DeepStoragePlus.

I'll try my best to list all changes made, but I cannot guarantee it, so please check the Files tab for all changes.

This PR, when merged, will require the usage of a new Resource pack:
DeepStoragePlus.zip

I personally recommend using a site such as https://mc-packs.net as it's by far the most easy to use option out there.
The resource pack has already been uploaded and can be downloaded under the following link:
https://mc-packs.net/download/59195941485ccb77792854e7e8e7d9d521822403

WARNING!

While I did some minor to large testing of the DSU, IO Filter and Sorting GUI will I NOT guarantee that everything works. Testing it yourself is HIGHLY recommended to avoid any unnoticed bugs or glitches. Thanks.

Also, this update will for sure break existing setups, which will either require some manual migration (or a simple new start) from the server owners, or a migration system in the plugin to allow the switch.

Changes

• Improved custom Item System!
  • Items now use CustomModelData values for the textures
  • Added custom items for empty Storage Container slots, empty Link Module slots and for the walls.
    Preview: https://cdn.discordapp.com/attachments/664583111308214304/920822126628442192/unknown.png
• Improved custom Item checks for Inventory. Now it checks for custom model data instead.
• Added an ItemBuilder class to simplify(?) Item creation. Also gets rid of some duplicate code.
• Improved code at some places. Mainly added extra null checks to get rid of IDE errors. Also fixed the int text[] thing.
• Updated download URL to the new one.

[Andre601]

Made some more noticable changes:

• Switched the ItemBuilder class out for a per-class Item creation. Now each custom item has its own class for creating the item stacks.
• Added custom textures for speed upgrade. It now also has a own texture.
  • This also means that the resource pack has changed. New URL: https://download.mc-packs.net/pack/3e75a48eef23419d26aef24fc95710dca75ff7f2.zip
• Switched Storage Containers from GOLDEN_AXE to MUSIC_DISC_13, which is also unstackable, but doesn't cause high damage when left-clicking entities.
  • One current downside is, that the music is displayed. Need to find a solution to get rid of this...

[Andre601]

I think I found the perfect item for storage containers now: Iron Horse Armor!

It is non-stackable, doesn't have any weird attributes in its lore (music disc), doesn't alter the texture (potion) and exists for ages now.

This also means that a new Resource pack has been made to support it:
https://download.mc-packs.net/pack/65ada59a809af41a24c2036663a291c30d8cb70b.zip