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
Remove empty ActiveField errors and fix bootstrap templates
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
Merge pull request #3285 from mikehaertl/master

Fix bootstrap templates
Fix #3265

Adding a new additional validation rule in the gii-crud generator enforcing the expected format.
Update CHANGELOG.md
Fixed regex-escaping in crudgenerator
Updated links to guide pages