16649 general contrast issues

[andrewgormley]

Fixes: #16649

• (Footer) Date and version text low contrast [dark, global]

• (Header) Secondary text low contrast [dark, global]

• (Racks) Low contrast labels [both, multiple]
  Leaving labels off this task for now, per our last discussion about labels needing to stay the same colors.

• (Object) Low contrast on object title sub items eg. created 2020-10-10 [dark, multiple]

• (Misc) Low contrast on form error text [both, multiple]
  Fixed for light. Dark mode is not possible with the current fontsize, and colors.

• (Toast) Low contrast for warning toast [light, multiple]
  Improved the WCAG contrast score but not quite to AA standard as orange on light bg are both classed high contrast colors according to WCAG but this is okay with the warning visual aids

• (Misc) Low contrast on placeholder module placeholder text [dark, multiple]

[andrewgormley]

This PR needs to be reviewed in a sequential order, please review #16750 and #16751 first.

[jeremystretch]

Thanks @andrewgormley!

I have one minor concern regarding the submenu headings in the navigation menu: At first glance it feels difficult to distinguish the headings from the link items as they're very similar in color.

[jeremystretch]

Just noticed another issue: The card headings are the same color as the page behind them:

[andrewgormley]

@jeremystretch thanks for the review, I've fixed the issues. Regarding the navigation sub headers, I can definitely see what you mean, I've changed them to a primary color and updated the border to match, let me know what you think.

I've also included another small change to update the footer icon colors which we forgot to include as a sub-task.

[jeremystretch]

Thanks @andrewgormley, looks good!