Updated Forge versio to 2.5.1-SNAPSHOT.

This is to accomodate for changes in the ScaffoldProvider API,
specifically the isSetup() method.
Fix for NullPointerException thrown durin isSetup() invocation.

Also modified the signature of the implemented method as per the
new API.
FORGE-1822 Use the Project instance from the Context classes.

The ScaffoldSetupContext and the ScaffoldGenerationContext classes
now carry the selected Project instance in accordance iwth the
ScaffoldProvider SPI changes made in FORGE-1822.
FORGE-1825 Revoke the overwrite flag from scaffold commands.

The ScaffoldProvider SPI's context classes no longer carry an
overwrite parameter.
Modified the addon to depend only on APIs not IMPLs

The addon now depends on the RestGenerationContext and JPAFieldOperations
classes that are present in javaee-api.

Removed the javaee-impl dependency from the project POM.