Searchbox ADA Issues

[bbusenius]

Fixes #673

Changes in this request

• Added aria-haspopup="true", aria-expanded="false", and an aria-label to the button dropdown as well as an aria-labelledby attribute to the ul menu to improve how these elements are announced in screen readers.
• Removed aria-label="Limit the library catalog search" from select since it is being overridden by the Javascript mentioned in previous item.
• Removed aria-label="Search the library catalog" from input since this is redundant due to the preceding label.

[bbusenius]

@bluairis, I'll be curious how the changes to the search button dropdown are announced in your screen reader.