feat: stock portfolio backtest calculator

[neo773]

a.mp4

/closes #122
/claim #122

[neo773]

@Shpigford
This is ready to be tested and reviewed

[Shpigford]

@neo773 Looking good! Here's some feedback for you...

1. Z-index issue with search dropdown and form labels.
   

2. Clicking this should evenly distribute % across all the stocks. In this case, it'd set both to 50 %.
   

3. We shouldn't use alerts for errors. We should show the error inline in the form.
   

4. Search boxes should prioritize stock symbol matching first over the stock name.
   

5. Graph bottom legend not needed since it's at the top.
   

[Shpigford]

Getting there! A few more bits of feedback...

1. This always needs to be 100% (meaning the form shouldn't submit and we should show an error message when it doesn't equally 100%).
   

2. It's still using alert messages instead of inline.