SCHEMA-154. Makes KijiAdmin an interface backed by HBaseKijiAdmin.

Also adds a convenience method to InstanceBuilder for adding cell values
with the current timestamp.

Signed-off-by: Juliet Hougland <juliet@wibidata.com>
SCHEMA-105. Move KijiColumnPager to impl package

Signed-off-by: Robert Chu <robert@wibidata.com>