Change settings' spans to divs
Define JSlider.areSettingsValid()
Add getKeyCode() and isAnArrowKey() to ui.js

* simplify initInputsEvents()
Add #custom-width-template, format #settings

* use .input
* use .active instead of .disabled
Define initCheckboxesEvents() in ui.js

* use initCheckboxesEvents() to replace initAdvancedChangeEvent()
Move preview() to bottom in ui.js
Add isActive(), activate(), deactivate() to ui.js
Remove isAdvancedEdit() from ui.js

* remove checkboxes var too
Add initCustomTotalWidthInput() to ui.js
Add initCustomWidthInputs() to ui.js
Remove $advanced checkbox from main.js
Move getKeyCode() and isAnArrowKey() to top
Add reinitInputs(), remove canUpdate() from ui.js