add itemChooser plugin
updating default layout and elements

- adapt Common/admin_index
- include choose.js in admin layout
- include chooser field in default search element
change Links/admin_form to use chooser
updating Node chooser implementation

also renames Nodes/admin_links to Nodes/admin_chooser
implement Block chooser
change Attachment/browse to use admin_popup layout
implement User chooser
adding chooser usage example
remove implicit addition of Paginator

helpers are lazy loaded in 2.3 and skipping implicit addition here
allows plugins to use an alias for Paginator helper
search: update button urls to use 'querystring'
use ^= (starts with selector)
moved JavaScript code out of TinymceHelper. now keeps RTE related code in `Croogo.Wysiwyg`.
the Wysiwyg plugin.
moved fields configuration to Wysiwyg plugin.
dependencies loaded first.

There could be scenarios where Tinymce appears before Wysiwyg in Hook.bootstraps. But Wysiwyg is a dependency plugin of Tinymce. In that case we need to reorder the list of plugins to be loaded.

This could become a part of a lib in the future or done in Extensions plugin whenever a plugin is activated/deactivated.
Updating view fallback mechanism

For plugins that extend NodesController, we should allow fallback to
use views from core Nodes plugin (if none is found in current theme).
adding tests for _viewFallback
Merge remote-tracking branch 'rchavik/1.5-plugin-view-fallback' into 1.5
add $showActions allowing hiding of actionsBlock

to hide 'actions' block:

	$this->set('showActions', false);

in the view.

Fixes #346
avoid adding 'current' class to multiple menu item

eg: navigating to '/admin/settings' would mark all Settings submenus as
current. this change would make only the first item as current.

fixes #345