Streamlining component event listeners

[mgarin]

There are a few inconveniences with different component event listeners such as:

• Inconsistent information on what actually happened in the event
  Most of the newer listeners (added recently in new or reworked components) are fine, but a lot of older ones aren't. For instance WebDateField's DateListener doesn't provide old date which is certainly needed for any change-type listeners. Some listeners don't provide any information at all, making their usage a nightmare in some cases.

• Inconsistent event handling on the component side
  The main issue is that there is no way to determine whether or not a particular event listener - for instance DateListener mentioned above - would trigger upon changing the value through the code. In most cases they will, but I'm pretty sure there was at least one or two exceptions somewhere due to use case.

• Inconsistent internal implementation of listeners
  This doesn't really affect WebLaF users, but it does make it way harder to maintain the code, so streamlining internal implementation of all event listeners would make my life easier and the code cleaner.

A few (somewhat) related issues:

• WebComponentPane drag doesn't work when content have mouseListener #531
• WebPathField does not notify PathFieldListeners when calling setSelectedPath #504
• WebImageDrop doesn't work properly on Mac OS X Sierra (10.12.1) #423