Add resourceUriTargetCache to SMW\SPARQLStore\RedirectLookup

XDebug profiling uncovered that repeated requests are made to the same
resource uri and to improve performance an in-memory cache is added to
avoid unnecessary DB lookup requests for already known uri's.
Add dataItemExportCache to SMW\SPARQLStore\TurtleTriplesBuilder

Improves performance especially when subobjects are involved.
Update SMW_LanguageZh_tw.php

Translation update kindly provided by [Linforest](https://semantic-mediawiki.org/wiki/User:Linforest)
Fix highlighting of results

SMWSearch did not supply search terms needed by MW to apply highlighting to the
search results. So MW's Searchhighlighter put an empty span between each and
every byte of the result snippets.

This patch will return a search term that will match on every line start of the
article text so that the highlighter will output the first few characters of
the first few lines of the articles contained in the search result

Those lines will be truncated after 75 characters or so, so this may not
really give the correct beginning of the article. It should be good enough as a
temporary solution.
Update en.json

Add missing system message (see issue https://github.com/SemanticMediaWiki/SemanticMediaWiki/issues/181)
Update qqq.json

Add system message description (See issue https://github.com/SemanticMediaWiki/SemanticMediaWiki/issues/181)
Merge pull request #505 from s7eph4n/master

Fix highlighting of results
Merge pull request #503 from SemanticMediaWiki/i18n-zh-tw

Update SMW_LanguageZh_tw.php
Merge pull request #487 from SemanticMediaWiki/sparql-redirectlookup-cache

Add resourceUriTargetCache to SMW\SPARQLStore\RedirectLookup
Update RELEASE-NOTES.md

[skip ci]
Merge pull request #506 from SemanticMediaWiki/i18n-188

I18n 181