New truncate and truncateWords methods

New truncate and truncateWords methods, https://github.com/yiisoft/yii2/issues/2941
Update BaseStringHelper.php

Length check.
Update CHANGELOG.md
Update BaseStringHelper.php

Updated to use mb_* functions
Test case for new truncate methods.

Test case for new truncate methods.
Update BaseStringHelper.php
Update apps-advanced.md

just a type correction and suggestion on adding a comma and one word (ie 'by') to make it more easily to be understand.
Merge pull request #3080 from castea-webdev/patch-1

Update apps-advanced.md
prepare for 2.0.0-beta release.
prepare for next release.
Some fixes for #3074 Hungarian translation
Gii model generator did not add correct db connection

if component id is different from 'db'
do not throw exception if db component is not set

without this the form does not allow choosing a different connection id
Merge pull request #3084 from pappfer/hungarian-translation-fix

Some fixes for #3074 Hungarian translation
Update UniqueValidator.php
Merge pull request #3085 from plusodinminus/patch-2

small typos changes
Fixed view path in debug mail panel
debug: fix highlight of redirect HTTP status

1xx status is not that common.
updated appd-advanced.md

added predefined path aliases of advanced yii application template
Merge pull request #3097 from Skullcrasher/master

updated appd-advanced.md