Add Web Query using Webpages in Worktable

[niutech]

This feature adds a new special search engine for Web Query widget: Webpages in Worktable. By setting this engine, the search query doesn't open SERP in your default web browser, but loads simultaneously in all Webpages in the Worktable which have QUERY placeholder in their URLs. See the following example:

Amazon Webpage URL: https://www.amazon.com/search/s?k=QUERY
eBay Webpage URL: https://www.ebay.com/sch/i.html?_nkw=QUERY
AliExpress Webpage URL: https://www.aliexpress.com/w/wholesale-QUERY.html

The branch is based on the Release 2.6.0-beta, for changes see the last two commits.

[alexk111]

It looks like the query-webpages branch was created from the Release 2.6.0 branch instead of master. This will merge all of the Rel 2.6.0 changes rather than the query-webpages ones.
This also makes it impossible to review the code changes made by that specific feature.

[niutech]

@alexk111 Done!

[alexk111]

Thanks for the update!
It looks like a "hackish" way to directly access DOM unrelated to the web query widget with css query selectors, which will cause many potential issues in the future.

I'll implement the feature with a proper inter-widget communication, so closing the PR.