508 compliance fix for upload widget (#2406)

* 508 fixes to bring the comments table into compliance. The <thead> element must be visible to users and <th> must display text that indicates what resides in the columns below.

* Updated to properly use the i18 translation

* This is a 508 Compliance fix to add a keyup.enter, role, and tabindex to both the icon and span associated with the file upload widget. This will allow keyboard-only users the ability to tab to a file loaded with the Upload Widget and select the element using the enter key.

ng2-components/ng2-activiti-form/src/components/widgets/upload/upload.widget.html

@@ -10,8 +10,11 @@
                             [id]="'file-'+file.id+'-icon'"
                             [src]="getIcon(file.mimeType)"
                             [alt]="mimeTypeIcon"
-                            (click)="fileClicked(file)"/>
-                    <span md-line id="{{'file-'+file.id}}" class="adf-file">{{decode(file.name)}}</span>
+                            (click)="fileClicked(file)"
+                            (keyup.enter)="fileClicked(file)"
+                            role="button"
+                            tabindex="0"/>
+                    <span md-line id="{{'file-'+file.id}}" (click)="fileClicked(file)" (keyup.enter)="fileClicked(file)" role="button" tabindex="0" class="adf-file">{{decode(file.name)}}</span>
                     <button *ngIf="!field.readOnly" md-icon-button [id]="'file-'+file.id+'-remove'" (click)="reset(file);" (keyup.enter)="reset(file);">
                         <md-icon class="md-24">highlight_off</md-icon>
                     </button>