POM-4. Add kiji-annotations library to dependency management of the root pom.

This commit modifies kiji-schema to comply with POM-4, which modifies the
Kiji root pom to include the kiji-annotations library in its dependency
management section.

Signed-off-by: Lee Sheng <lsheng@wibidata.com>
SCHEMA-122. Remove duplicate header.

Signed-off-by: Lee Sheng <lsheng@wibidata.com>
SCHEMA-20. Improve validation of cell schema changes.

Counters must specify schema storage 'final'.
Final columns require inline schema specifications and cannot change.
Schema storage cannot be modified.

Signed-off-by: Milo <milo@wibidata.com>
SCHEMA-66. Annotate interfaces for client subclassing.

Marked all interfaces and abstract classes as @Sealed or
@Extensible to tell users how they should use them.

Signed-off-by: Milo <milo@wibidata.com>
SCHEMA-114. 'kiji install' can cause a NullPointerException.

- KijiURI validates instance and table names.
- KijiInstaller checks that KijiURI specifies an instance name.

Signed-off-by: Christophe Taton <taton@wibidata.com>