Let's deprecate BLOCK_NOT_AVAILABLE_TEXT

This define contains a localized text to be shown when a block is no
longer available.
Let's deprecate it since:
1. after calling Localization::changeLocale() this define contains a text
in the wrong language.
2. there's no reason to have manage this text represented with a define
whereas all the other messages are represented directly
Add phpdoc to signal return type of Loader::db

Adding the return type allows auto-completion systems
to automatically suggest methods and properties.
Unify jQuery ready syntaxes in i18n translations
Remove leading zeros from date format in i18n finnish datepicker translation
Fix changed row's indents while we're at it
Merge pull request #1469 from ojalehto/change/i18n/finnish-date-format

Remove leading zeros from date format in i18n finnish datepicker translation
Merge pull request #1457 from ojalehto/refactor/i18n/unify-jquery-ready-syntaxes

Unify jQuery ready syntaxes in i18n translations
Merge pull request #1453 from mlocati/patch-5

Add phpdoc to signal return type of Loader::db
Merge pull request #1383 from mlocati/deprecate-useless-constants

Let's deprecate BLOCK_NOT_AVAILABLE_TEXT