Debounce requests in ServerDataSource

[uap-universe]

Discussed in #141

The goal is to reduce the number of HTTP requests when the filter is changed.

[uap-universe]

The topic seems to be a bit more complicated than just debouncing the request.

First observation is, that events are not fired on every key stroke when typing text in a filter. So the number of requests is already not immediately problematic.

However, when the change is recognized, the whole process results in resetting the filter to the state it had before firing the event.

Example: let's say you have a column and type in the text "foobar".

1. f is entered, nothing happens
2. o is entered, nothing happens
3. o is entered, nothing happens
4. b is entered, change is fired (text is currently foob)
5. a is entered, change is processed, query is running
6. result is received, table is updated, filter is reset to foob
7. r is entered, but because of the reset, the filter text is now foobr instead of the intended foobar

I don't have a clue how to fix this easily. You can always have bad timing, even when you add some waiting times. Therefore, I guess, the whole thing would need a major rework.