WICKET-5024 Global ajax event for precondition is not called
WICKET-5024 Global ajax event for precondition is not called

Remove logging
WICKET-5027 no need for huge if-else in FormTester when
ListMultipleChoice,
CheckGroup, RadioGroup and Select have properly implemented
getModelValue()
Warnings cleanup.
No functional changes!
Fix jshint problems in ajax.js
Fix jshint problems in head.js
Fix jshint problems in dom.js
Fix jshint problems in event.js
Fix jshint problems in fonm.js
Fix jshint problems in channel.js

Use higher order functions to be able to properly count which callback is called and which not
Add the JS tests in Grunt lint checks
Improve the test for ChannelManager#drop(). It should work with higher order functions too.
JSDoc improvements

No functional changes
WICKET-5025 Set the component as a context to the ajax listeners
Javadoc improvements - move the Javadoc from a field to its getter method. Otherwise it doesn't appear in the generated html.
WICKET-4861 Making MultiFileUploadField use HTML5 multiple attr & remove confusing fakepath
Merge branch 'master' into reference-guide
Merge branch 'reference-guide' of https://github.com/michaelmosmann/wicket into reference-guide

Adds initial docu for models
Fix minor warnings in the generation of the docs
Merge remote-tracking branch 'upstream/reference-guide' into reference-guide