Updates to improve versatility in implementation

[HaSistrunk]

Closes #199 , #200 , #204 , #205 , #206 , #203

Updates the Style Library and Guide identified as necessary from aquila and argo styles implementation. Documenting the changes in detail here to make implementation back into sites easier.

Global changes (fixes #204 ):

• Change link--bold class to text--bold for wider application
• Give input__error class a width of 100%
• Add a new helper class flex--column to apply flex-direction: column styles to a flex container
• Move bottom padding from h2 to heading--dotted-border class.

Form improvements (fixes #199 ):

• Groups form components in Style Guide
• Remove hidden labels from basic text inputs (better UX and a11y to avoid hiding labels)
• Add basic custom styles for select, input, and textinput styles
• Increase form error message font to 14px
• Remove unused classes from inputs
• Remove aria-required="true" from the search component. We only need required like the other inputs have (fixes #203 )

Make cards more flexible (fixes #205 ):

• Add a card--container class to apply to cards that aren't clickable to change their hover/focus styles.
• Remove list--unstyled from card HTML and add to card scss instead.

Improve header dropdown (resolve #206 ):

• Add z-index to mobile nav dropdown to keep other page content from covering it.
• Remove tabindex="0" from nav mobile dropdown button and add ids for scripts (dropdown__list--mobile). We can take a closer look at this when we standardize our scripts in the style library.

Simplify pagination (fixes #200 ):

• Remove unused attributes and improve accessibility