New 'change' check mode + new 'check_modes' option

[bmurashin]

Completely removed check_mode Scalar option. Introduced a check_modes Array option for replacement. Introduced a change validation mode. Updated docs.

P.S. Did no handling for using former check_mode option as Symfony will throw an InvalidConfigurationException itself. If there's need for more informative exception message like 'This option deprecated, use a new one instead', I can code and submit it in a new PR.

[Abhoryo]

Please add the exception + delete check_mode: false in the documentation.

Update directly this PR.

[bmurashin]

updated

[Abhoryo]

thx