Diem 5.0.0_ALPHA3

This third Alpha release fixes 14 bugs, and provides a better support for Diem extension with symfony plugins.

• added a plugin system
• created dmWidgetGalleryPlugin
• moved dmLayout admin module to Tools namespace
• reduced admin chart lifetimes in admin services.yml
• moved core app.yml
• made LICENSE file more readable
• improved french translation
• moved page guessing to dmFront/page action
• fixed programmatic forward404
• fixed json encoding on upload ajax responses
• switched to ALPHA3
• added dmForm->getHelper() method
• added PluginDmPageTable? findOneBySlug and fetchError404 methods
• fixed install password when database has no password
• made dmHelper->£media more robust
• added core thumbnail web service ( secured )
• removed deprecated w3cValidation
• added folder synchronization on front media bar
• allowed front link droppable inpu to accept only pages or medias
• added an error dialog for debugging ajax responses
• added the jQuery loadStylesheets plugin
• added the widget_renderer service
• allowed front widget views and forms to declare their required assets, so they can be loaded asynchronously
• fixed media widget default resiz method
• fixed widget_width value on front widget forms
• added quality field to media, text an gallery forms
• added dmWidgetType->getPublicName method
• made dmWidgetTypeManager more robust
• simplified a lot dmFrontInitFilter
• refactored front page helpers to use the new widget_renderer service
• improved widget edit dialog titles
• cleaned dmFrontActions code
• refactored dmWidgetActions to use the new widget_renderer service, and serve widget assets asynchronously
• made front code editor use the new error dialog
• made jQuery dmFrontForm linkDroppable method public
• fixed admin menu order