…T claims

This commit replaces the usage of java.util.Date with java.time.Instant in handling JWT claims. This means upgrading from JDK7 to JDK8. This is done for better adherence to ISO 8601 standards and better precision in time-related operations. Classes working with claims have been updated to use the newer Instant class, providing better precision and cross-timezone compatibility. Additionally, overloading convenience methods for setting OffsetDateTime and ZonedDateTime on top of Instant have been added on the JwtBuilder and DefaultJwtBuilder.

The JWT handling has been updated to default to Java's Instant class. This change removed support for various date and time classes such as ZonedDateTime, OffsetDateTime, Date, and Calendar in favor of an Instant-based approach throughout the codebase. The appropriate tests and documentation were updated to reflect this change.

Replaced all instances of 'Date' with 'Instant' in JwtParserTest to more accurately reflect variable usage. Also added a TODO in JwtDateConverter.java to clarify the handling of epochMillis vs epochSeconds.

This commit updates the version of the project across all pom.xml files from 0.12.4-SNAPSHOT to 1.0.0-SNAPSHOT as it prepares for a major release. Changes cover the core project and various extensions, signaling a coordinated upgrade across the codebase.

All instances of java.util.Date in code have been replaced with java.time.Instant for better time precision and timezone handling. This includes changes in variable names, method names, test cases, comments and documentation. The java.util.Date-based utilities have also been removed.