Riven mod support

[Kaptard]

I'm submitting a...

• [ ] Bug report
• [x] Feature request
• [ ] Documentation issue or request

Current behavior

Riven mods aren't supported at all.

Expected behavior

Add the following support for riven mods:

• Price tracking
• Trading
• Evaluation (Grading like Therox' bot does, and DPS calculation)

Minimal reproduction of the problem

The need for price tracking and trading support are trivial, so I'll only explain the Evaluation bit.

Imagine you just got a riven mod. You don't really wanna use it, so you wonder what it's worth. Since there are so many riven mod variations, you're gonna have a hard time judging a price. Ultimately, your decision on the price is based on vague notions, not hard numbers.

To solve this, riven grading, meaning the evaluation of how strongly an attribute expresses itself will be important in determining the min/max values for possible DPS. Based of that value, we should display the DPS values of the mod, as well as what would be possible with a different grading.

Design implementations may vary, there are a lot of ways to do this one.

Environment

Browser:

• [ ] Chrome (desktop) version:
• [ ] Chrome (Android) version:
• [ ] Chrome (iOS) version:
• [ ] Firefox version:
• [ ] Safari (desktop) version:
• [ ] Safari (iOS) version:
• [ ] IE version:
• [ ] Edge version:

For development issues:

• Node version:
• Operating System:

Additional Description