Introducing Simple Resource concept.
Introducing simple resource concept which serves a single entity from a particular url path.

Fixing the collection level action client builder generation

Moved id check for client builders to AbstractRequestBuilder class. Added javadoc for ResourceLevel.ANY.

Addressing review comments.

RB=176567
BUGS=SI-787, SI-761
R=si-dev,jbetz,slim,bduncan,kjin,sihde
A=jbetz,kjin