New Feature: Update site url in Database

Signed-off-by: Deon Thomas <PrinceAMD.Elive@gmail.com>
added some debug
added some debug
added some debug
added some debug
added some debug
added some debug
fix typo
removed foolish debug
big reword and remove old code
updated option page
Fix PHP notice
Fix - error checking wrongly failed checks if database config label was not the same as site config label
Add option for hiding specific push options for all users (inc admin)
Add action hooks to allow other developers to extend SitePush.

Actions added:-

* sitepush_push_begin
* sitepush_pre_push_files
* sitepush_post_push_files
* sitepush_pre_push_db
* sitepush_post_push_db
* sitepush_push_complete

Note - these actions only run on the site where the push is being run from, not the destination site. To run code on the destination site you would need to use these hooks to send a command to the destination site, which triggers your code.
Make sure SitePush doesn't try to deactivate itself
Add constant SITEPUSH_HIDE to allow SitePush interface to be completely hidden in any given site.

Add define('SITEPUSH_HIDE',TRUE); to wp-config to hide SitePush for that site.
Update/improve help text in SitePush options screen
Add comments to highlight code which won't work on Windows.
Updates to readme file