Patch for "Panel for Joins in the Graphic Query Builder"

Hi All,

As per my discussion with Dave Page:
- Replace the generic dialog box that the graphical query builder uses when
  you right-click a join, and select the join type option. It currently uses
  an ugly standard dialog. Create a more compact and purpose built one - like
  the one you get when you add criteria, and click on the 'restricted value'
  button.

Modifications and addition are as follows:
* Introduced couple of new classes for handling operations:
  + gqbJoinsPanel - Panel for handling the joins in the tab - container for
                    criteria, order & columns panels
  + gqbJoinsPopUp - Pop up window, when selecting a column from the table list,
                    derived from the gqbColsPopUp
  + gqbGridJoinTable - Table for handling all the joins data. It handles three
                       columns Source, Join-Type & Destination
* Added new images gqbAdd.xpm & gqbRemove.xpm
* Renamed wxRestrictionGrid to gqbCustomGrid as we're using the same Grid for
  handling the criteria(s) and join(s) in the gqbCriteriaPanel and gqbJoinsPanel
  respectively.
* Added one operator [] in gqbArrayCollection for accessing the gqbObject object
  directory (replacement/accessibility of the object at particular index will be
  easy and fast).
* Removed the context menu "Set Type" removed for join, as this operation will be
  handled from the joins-panel now onwards.

Regards,
Ashesh Vashi