Change <code>array_reduce</code> with anonimous function variant to easy string collection from pieces of unions.

Using short array syntax.

Add test for UNION/UNION ALL function.
It could be useful to use "phpunit --group=db --filter testBuildUnion" command for run it.

Change buildUnion method to be ready to accept parameters in <code>['all' => $all, 'query' => $query]</code> format for division to "UNION" and "UNION ALL" constructions.

Change passing parameters to array with two elements – 'all' which means if we use UNION or UNION ALL construction and 'query' which is our sql query that will be at right of construction.

Forget one ";" :D

Delete some spaces from result string.

Change union method to accept also <code>$all</code> variable. TRUE means that we must results <code>UNION ALL</code> construction, FALSE – that <code>UNION</code>.

Fixed some errors – syntax with ";" after closure function and also moved building of unions queries into this function.

Change using of implode to convert array of queries to union to array_reduce. Result of this changing is that code feel difference between two selects that connects with UNION and two selects that connects with UNION ALL.

#2103 improves http exception consistency and adds new subclasses

Adjustment the translation into Portuguese of Brazil.

Added ability to get incoming headers

Fixes #1958: `beforeSubmit` in `yii.activeform` is now executed after validation and before form submission

Transfer beforeSubmit function after global validation all fields forms

Conflicts:
	apps/basic/tests/README.md
	apps/basic/tests/unit/models/LoginFormTest.php

Greek core translation

fixes #1864

Minor fixes in active-record.md