[ticket/12597] Command for executing all available cron tasks

Command cron:execute-all executes all available cron tasks.
Test files in tests/console/cron folder

PHPBB3-12597
[ticket/12597] Improvement of test files

PHPBB3-12597
[ticket/12597] Correcing coding style mistakes

PHPBB3-12597
[ticket/12597] Add doc blocs in execute_all.php

PHPBB3-12597
[ticket/12597] Correcting bug in cron.php

PHPBB3-12597
[ticket/12597] Fix various refactoring mistakes

PHPBB3-12597
[ticket/12597] Update pull-request

Removes a useless comment.
Switchs command name from cron:execute-all to cron:run-all.
Replaces assertEquals by assertSame

PHPBB3-12597
[ticket/12597] Change EXECUTE to RUN in language

Fix previous commit : change execute to run in language keys

PHPBB3-12597
[ticket/12597] Fix misplaced release of db lock

PHPBB3-12597
[ticket/12597] Modification of return statuses and of test files

PHPBB3-12597
[ticket/12597] Fix constructor bug and servral doc blocs

PHPBB3-12597
[ticket/12597] Fix various problems

Actually fix the return status of command cron:run-all
Fix some doc block coding style issue
Fix missing and obsolete file headers
Delete a useless constructor method

PHPBB3-12597
[ticket/12597] Changes name of command  cron:run-all to cron:run.

Also adds an optional argument to specify one precise cron task to
lauch, and modifies test file accordingly.

PHPBB3-12597
[ticket/12597] Fix coding style and typing mistakes

PHPBB3-12597
[ticket/12597] Fix language key name

PHPBB3-12597
[ticket/12597] Refactoring and test improving

Adding tests of return status
Refactoring code
Adding consistency in verbose mode

PHPBB3-12597
[ticket/12597] Fix visibilty of two functions in run.php

PHPBB3-12597
[ticket/12597] Fix various mistakes

Typing mistakes
Coding style issue
Verbose mode messag

PHPBB3-12597
[ticket/12597] Fix various mistakes

Typing mistakes
Coding style issue
Verbose mode messag

PHPBB3-12597
[ticket/12597] Typing corrections and improvement of code consistency

PHPBB3-12597