support the idea of mod dependencies

[seiyria]

dep management interface should:

• have a url box, and an import button
• a list of deps (ability to remove, show basic metadata)
• cached deps in the resources folder
• item/npc picker need to support showing other dependent things
• since the content repo will be cloned as part of the general resource acquisition process, add a button to quickly import base game content and reference the content-downloaded one
• a button to update mod dependencies