Introduce ignoringClasspath option in SpringLiquibase.

This backwards-compatible change will allow to perform "classpath:"-prefix-insensitive comparisons between inserted changesets and parsed changesets, by adding new option "ignoringClasspath" in SpringLiquibase bean configuration.

This can be useful in situations where Liquibase changesets are executed with Spring and another plugin (such as Maven).

Only `ShouldRunChangeSetFilter` currently makes use of it. 
Default value for this new option is false, which corresponds to the former behavior.
If set to `true`, this will impact migration execution via `SpringLiquibase` and `Liquibase#listUnrunChangeSets`.