initial code for extensions and hooks
add more files to example extension
remove empty line
call hooks 'preRemoveDocument' and 'postRemoveDocument'
call parent::show
base clase for extensions
Merge branch 'develop' into hooks
Merge branch 'develop' into hooks
Merge branch 'develop' into hooks
Merge branch 'develop' into hooks
Merge branch 'develop' into hooks
added hook before adding a document
added initial class for hooks
Merge branch 'develop' into hooks
new class to manage extensions
file for setting up extensions
add more examples for hooks
fix name of class
add method callHook()

this method is ment to be called from the view classes. It checks
for a hook set up for the current view.
added method show()