Get DB unique indexes information

Proposal for #66: auth client implementation

Fixes #1610: `Html::activeCheckboxList()` and `Html::activeRadioList()` will submit an empty string if no checkbox/radio is selected

extended from codeception testcase, added docs

Gii should keep horizontal layout

Bootstrap's dropdown encodes also trailing caret tag

doc fix

Fixed sequence id match for postgresql

PgAdmin generates   sequence as  '"Schema"."Table_seq"'::regclass  when
non public schema is used.

Fixes #1499: Added `ActionColumn::controller` property to support customizing the controller for handling GridView actions

Added support for tagName and encodeLabel parameters in ButtonDropdown