UX: Improve app responsiveness/state accuracy through mouse pointer changes

[alexbfree]

As Paul reported experiencing in Digipower Live 3, and I have experienced it too, when you are dealing with large archives (Facebook & Google for example) the UI can appear to lock up or to have not registered your click. Whereas in fact it has registered your click and is just processing through a large set of data. This can result in you clicking a tab twice or not being sure what is happening.

Even without addressing [performance issues](#1011 etc.) we can massively improve the situation with some UX tweaks - by making sure the app always accurately shows when it is busy and when it is not.

To do this, I suggest the following:

1. Establish a "click handler" routine.
2. All clicks on tabs, filters, load buttons, basically anything that might result in large data processing or data transfer operations, gets refactored to use the click handler.
3. Within the click handler, the first thing that is always done, before processing, is to set the cursor to arrow with hourglass (cursor:wait in CSS terms)
4. when the processing is complete/tab loads/etc, the hourglass is set back to normal arrow (cursor:default in CSS terms)

Step 4 could be achieved by passing a callback function into the click handling code at stage 2 - to avoid replicating cursor change code in multiple places.

By changing the cursor to instantly reflect that the app is responding to your click and is busy, there should be no ambiguity about whether the app is working during slow operations.