Corpus Viewer: Add delay on search

[ajdapretnar]

Describe the bug
For larger corpora, instant searching works extremely slow. This is because search aims to show the results on the fly.

To Reproduce
Steps to reproduce the behavior:

1. Corpus (friends transcripts)
2. Corpus Viewer (search for a word)

Expected behavior
Search is a bit smoother.
Perhaps not showing results for every stroke of the key.
Option 1: Query is run on Enter.
Option 2: Implement delay on search (if no new character is added within some timeframe, run the search)

Orange version:
3.30.dev

Text add-on version:
1.6.0

Screenshots
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Operating system:
OSX

Additional context
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