Adds import/export decks feature

[willroberts]

Summary

Adds "Export Decks" and "Import Decks" buttons to the Collection screen. "Export Decks" copies decks JSON to the user's clipboard, and "Import Decks" provides a text box to paste JSON into.

Closes #224.

App changes (app/, etc.):

• Adds exportDecks and importDecks functions to InventoryManager
• Adds import/export buttons and handlers to the Collection view
• Adds new dialog windows for importing and exporting decks
• Tweaks startup logging a bit
• Comments more unreachable code

Server changes (config/, server/, worker/, etc.):

• Adds getDecksAsJSON and putDecksFromJSON methods to DecksModule
• Adds /api/me/decks/export-decks and /api/me/decks/import-decks routes
• Removes the custom StackLogger class

Build changes (docker/, gulp/, scripts/, etc.):

• Removes the pretty-error dependency
• Speeds up localdev rebuilds by retaining node_modules

Testing

Have you have tested your changes in the following scenarios?
Feel free to check off scenarios which don't apply.

• Starting backend services locally with docker compose up succeeds.
• I am able to create a new user and log in locally.
• I am able to complete a practice game locally.
• I am able to complete a purchase of Orbs, etc.