Fix: Allow "Show alt text" to work in Notify and Drawer (fix #119)

[swashbuck]

Fix #119

Fix

• Fix bug when using "Show alt text" where annotation icons were not shown in Notify popups or Drawer. This changes where in the DOM the annotations appear. Previously, they were appearing underneath Notify / Drawer. I could not find a simple Less-based fix for this.
• Fix incorrect class name syntax and remove comma: 'is-right, is-bottom'
• Removed reference to invalid h7HTML tag. Created HEADING_SELECTOR constant to avoid repeating values.
• Fix misspelling of computeAccessibleName().

Update

• Improve annotation display. Icon is now a square instead of a strange, oblong shape. Added padding to the tooltip text part to increase readability.

Previous

Improved

[swashbuck]

This is potentially an over-engineered solution, so there may be a better way to address it.

[kirsty-hames]

Works as expected thanks @swashbuck and the display is much better 👍