Credits groundwork

What have you done in this MR?

• Added the ability to award credits from a CSV file with an ingame command (ADMIN)
• Added the ability to modify an individual user's credits (PMOD)
• Added ContentAPI methods for working with credits
• Corrected a source of syntactic confusion in the login decoder (no actual change in behavior)

Are there any tricky things testers should keep an eye out for?

• No

• Yes, as follows:

• I have tested these changes thoroughly.

• This requires extra testing due to changes to architecture or other similarly risky changes.

• I used the Thanos Tool for any JSON edits, I did not edit any JSON files by hand (MR will be rejected if there are manual JSON edits).

• I acknowledge that this contribution will be released under the AGPL license.