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 BaseStringHelper.php
Changelog update
setting writable folders in init-script

It is said, that these folders are handled already by composer.json, what is definitely true. But if I can't (or don't want to) call composer create-project command, I have to run post-create-project-cmd manually like `composer run-script post-create-project-cmd`. IMHO, it's consistent to make such preparations in init script.
no need to set writable folders for console
removed unnecessary lines regarding writable dirs
Lithuanian translation
Reorganized guide.
guide wip [skip ci]
finished upgrade chapter [skip ci]
added case insensitve LIKE to PostgresQueryBuilder

fixes #3252

also improved unit tests for querybuilder buildLikeCondition
filterWhere for postgres ILIKE

fixes #3252
overwrite -> override
Merge pull request #3290 from crtlib/master

[ci skip] overwrite -> override
Merge pull request #3235 from crtlib/patch-5

setting writable folders in init-script