PDB-1585 - Can't tie a dashboard prompt to a content's parameter - UI doesn't show dropdown

@rfellows:
* This is a **poor man's fix** - removes the horizontal cell paddings that mess-up the layout of the gwt-ScrollTable and prevent the user from seeing the drop-down arrow;
   **restores functionality at the cost of appearance**.
* What's happening is that the the way that the gwt widget _CustomListBox_ is using a style="100%" attribute in its top-level element.
* The CustomListBox control is within a td of "#propertiesPanelParameterAssignmentTable .gwt-ScrollTable" - the GWT/HTML representation of a XUL <tree> (of ddMainFrame.xul).
* The styles in the globalCrystal.css are applying paddings to the td -> 100% + 20px padding -> causes the drop-down arrow to appear of the cell.
* One way to fix this right would be removing the fixed style="width:100%" that is being set (somewhere???) in GWT code, and applying that as a default, in CSS instead: <br/>
  <pre>.custom-list: { width: 100%; }</pre>
  Then, as a CSS override to this _CustomListBox_ only:<br/> 
  <pre>{ left:0px, right:0px; padding-left: 10px; padding-right: 10px; }</pre>
  Also, to be able to correctly apply paddings to the table headers' text, without unwantedly enlarging the table width,
  each header text would need to be wrapped in a block element, and margins to it applied instead.