Merge #11015: [Qt] Add delay before filtering transactions

Summary:
7b137aced [Qt] Add delay before filtering transactions Fixes 3141 (Lucas Betschart)

Pull request description:

As discussed in https://github.com/bitcoin/bitcoin/issues/3141.

This adds a QTimer pause of 200ms before start to filter so it should be possible to filter big data sets easier.

Tree-SHA512: ee599367794eac2c5b8bc7ecac47f44295e40c0ff543ff2f2c4860590f917b59b1cfb273fa564e6eb4c44016c0ef412d49f1a8f1b36b07e034022f51bb76653c

Backport of Core PR11015
https://github.com/bitcoin/bitcoin/pull/11015/

Test Plan:

make check
./bitcoin-qt -> transactions -> enter a filter

Reviewers: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D3832