Extract tests to separate project under the main POM and extract test utilities to a reusable library

[bsbodden]

The current directory structure:

redis-om-spring
\_ redis-om-spring ==> builds JAR redis-om-spring
    \_src/test/java  ==> currently has all tests and test utility classes
    \_src/test/resources
\_demos
    \_roms-documents
    \_roms-hashes
    \_roms-permits

Proposed directory structure:

redis-om-spring
\_ redis-om-spring ==> builds JAR redis-om-spring
\_ roms-junit           ==> will build test library (redis-om-spring-junit)
\_ tests                    ==> move the tests here and use (redis-om-spring-junit) to test
    \_src/test/java    
    \_src/test/resources
\_demos ==> add tests using redis-om-spring junit to all the projects under demos (see issue #37 )
    \_roms-documents
    \_roms-hashes
    \_roms-permits