Accessibility fixes for atlassian-editor bundled plugin

Problem Definition

Currently there are a few accessibility issues with the templates for this plugin, for example:

• editor-precursor.soy
  Add label to input and remove title attribute Add aria-label to .metadataButtons
• editor-quit-dialog.soy
  add assistive text to button
  TO DO convert to aria-label
• color-picker.soy
  add assistive text to "a" tags that look for the color names in i18n.properties
  TO DO convert to aria-label
• atlassian-editor.vm
  add aria-label to toolbarIconButton "a" tag
  Add label to wysiwygTextarea and editor-html-source
• i18n.properties
  Add color names