Do an accessibility audit

[noahmanger]

We've been adding so much stuff, but the major components are more or less in place. We should do an audit of the accessibility of openFEC.

[noahmanger]

I made a bunch of changes as noted here #723

Remaining task is to have Nick go through and double check my work.

[noahmanger]

Remaining questions:

• Do we need aria-controls or aria-expanded on the panel / rows ? - "it would be fine if the label was expand total receipts, expand total disbursements"
• Do we need aria-controls to accordion buttons and toggles?
• Where should the "Skip nav" button take the user? There's some disagreement on this.

[noahmanger]

Added aria-controls to the toggles.