Syntax Highlighting and Validation for embedded CRON expressions

[BoykoAlex]

Support syntax highlighting, for embedded CRON expressions:

@Scheduled(cron = "0 */30 * ? * *")

@Scheduled(cron = "0 0 10 * 1 1")

(See support for CRON in IntelliJ: https://www.jetbrains.com/help/idea/scheduled-tasks.html)

[BoykoAlex]

Fixed with 790d50f