webadmin,userportal: Small code improvements

1. Hard-coded strings for DOM events such as "click"
   replaced with constants such as BrowserEvents.CLICK

2. Removed unused CSS file: IVdcQueryableCellTable.css

3. Small code improvements in ResizeableCheckboxHeader
   (making field private and final)

4. Added Javadoc to ColumnResizeCellTable.wrapHeader

5. When comparing constant (non-null) vs. dynamic
   (nullable) value, it's always better to do:

      if (constant.equals(dynamic)) ...

   instead of:

      if (dynamic.equals(constant)) ...

   to avoid potential NPE if dynamic == null

Change-Id: Id8bfb32a64c6e6edfe62e92796b1a0ffad2e1141
Signed-off-by: Vojtech Szocs <vszocs@redhat.com>