Fix comment accessibility

1. Make the title a label (we won't need a title for seeing users
anyway, the full text is there).

2. Remove invalid `|| undefined` in the ng-disabled check

frontend/app/components/work-packages/work-package-comment/work-package-comment.directive.html

@@ -25,7 +25,7 @@
             class="inplace-editing--trigger-container"
             span-class="inplace-editing--container"
             link-class="inplace-editing--trigger-link"
-            link-title="{{ ::vm.text.editTitle }}"
+            aria-label="{{ ::vm.text.editTitle }}"
             execute="vm.activate()">
             <span class="inplace-edit--read-value"
                   ng-class="{'-default': fieldController.isEmpty()}">

frontend/app/templates/components/accessible_by_keyboard.html

@@ -1,7 +1,7 @@
 <a data-ng-click='isDisabled || execute()'
    role="link"
    class='{{ linkClass }}'
-   ng-disabled="isDisabled || undefined"
+   ng-disabled="isDisabled"
    title='{{ linkTitle }}'
    aria-label="{{ ariaLabel }}"
    data-click-on-keypress="[13, 32]">