Introduce ignoringClasspath option in SpringLiquibase.

This backwards-compatible change will allow to perform "classpath:"-prefix comparisons between inserted changesets and parsed changesets, by adding new option "ignoringClasspath" when configuring SpringLiquibase bean.

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`.