Add support for cypher check precondition in Cypher formatted files

[fbiville]

This will require a change to liquibase.parser.core.formattedsql.FormattedSqlChangeLogParser to make it extensible. The error currently looks like this:

liquibase.exception.CommandExecutionException: liquibase.exception.ChangeLogParseException: The 'cypher-check' precondition type is not supported.

	at liquibase.command.CommandScope.execute(CommandScope.java:235)
	at liquibase.ext.neo4j.e2e.PreconditionsIT.runs migrations depending on Cypher result(PreconditionsIT.groovy:64)
Caused by: liquibase.exception.ChangeLogParseException: The 'cypher-check' precondition type is not supported.
	at liquibase.parser.core.formattedsql.FormattedSqlChangeLogParser.parse(FormattedSqlChangeLogParser.java:577)
	at liquibase.command.core.helpers.DatabaseChangelogCommandStep.getDatabaseChangeLog(DatabaseChangelogCommandStep.java:100)
	at liquibase.command.core.helpers.DatabaseChangelogCommandStep.run(DatabaseChangelogCommandStep.java:77)
	at liquibase.command.CommandScope.execute(CommandScope.java:212)
	... 1 more