exposes the showDialog box through the SearchReplace command

allows the dialog to be called from outside the editor
Fixed bug where an exception was thrown when inserting images if valid_elements didn't include an ID for the image.
Fixed so empty strings gets passed to compressor instead of undefined.
updated to show lists and BR tags
Fixed bug where the advlist plugin wouldn't properly render the splitbutton controls.
Merge pull request #238 from danransom/patch-4

updated to show lists and BR tags
Added details for contribution to changelog.txt
Merge pull request #237 from danransom/patch-3

exposes the showDialog box through the SearchReplace command
Added back 3.x mceCodeEditor command to expose source dialog.
Fixed issue where custom_elements would not remove the some of the default rules when cloning rules from div and span.
Fixed bug where visual blocks menu item wouldn't be marked checked when using the visualblocks_default_state option.
Fixed bug where save button in save plugin wouldn't get properly enabled when contents was changed.