Guide start-hello in Russian
small fixes
\yii\i18n\DbMessageSource code style fixes
Merge pull request #3769 from creocoder/db-message-source-code-style-fix

\yii\i18n\DbMessageSource code style fixes
file validator added mime - types , image validator fixed
file validator tests added
Merge pull request #3762 from MUTOgen/guide-start-forms

Russian guide. Start forms
Merge pull request #3773 from Ragazzo/file_validator_adjusted

File validator adjusted
ensure guide PDF compiles with russian characters
fixed note about search class
Merge pull request #3775 from Ragazzo/widgets_guide_adjusted

fixed note about search class
sql view mapping added , similar to CQRS query model
fixed notes and guide
adjusted validator doc. [skip ci]
Gii generator for MongoDB Active Record created.
Docs about MongoDB gii generator usage added
Updated pt-BR translation
Merge pull request #3779 from wbraganca/master

Updated pt-BR translation
Fixed incorrect inheritance of search model
Adjusted Russian translation of forms guide section