Accessibility: EUI Tables

[aphelionz]

Subset of tickets in #614 that deal with the "Tables" category of EUI, anything that falls on or under this URL: https://elastic.github.io/eui/#/display/tables

• Select All Checkboxes on Tables Lacking Proper Labeling Select All Checkboxes on Tables Lacking Proper Labeling #746
• Singular Row Selection Checkboxes missing proper labeling Singular Row Selection Checkboxes missing proper labeling #747
• "Actions" Toggles not labeled correctly "Actions" Toggles not labeled correctly #748
• Temporal Contect Switches in Table Search and Filter Temporal Content Switches in Table Search and Filter #749
• EuiTableHeaderCell should read aloud text content instead of aria-label EuiTableHeaderCell should read aloud text content instead of aria-label #1378