Accessibility : Aztec Editor UI Improvements

[jd-alexander]

Accessibility Scanner audit

Each item corresponds to an outlined area on the attached screenshot below.

• Text contrast
  org.wordpress.android:id/title
  The item's text contrast ratio is 2.56. This ratio is based on an estimated foreground color of #87A6BC and an estimated background color of #FFFFFF. Consider increasing this item's text contrast ratio to 3.00 or greater.

• Text contrast
  org.wordpress.android:id/aztec
  The item's text contrast ratio is 2.56. This ratio is based on an estimated foreground color of #87A6BC and an estimated background color of #FFFFFF. Consider increasing this item's text contrast ratio to 3.00 or greater.