Property cache refactoring

Added PropertyCache object to consolidate property caching operations
Refactored element objects to use it
Added unit tests
Make element cache unit tests a bit faster
Merge branch 'cache-updates' into table-wrappers

Conflicts:
	src/main/java/edu/jhuapl/tinkerpop/AccumuloElement.java
	src/main/java/edu/jhuapl/tinkerpop/AccumuloGraph.java
Merge pull request #90 from JHUAPL/cache-updates

Property cache updates
Merge branch 'master' into table-wrappers
Existence check fixes

Added unit tests for skip existence checks
Bug fix for existence check in addVertex
Bug fix in InputFormatsTest
Was reusing the same fake Hadoop table name and causing problems with
existence checks
Merge branch 'master' into table-wrappers
Move vertex property loading to ElementTableWrapper
Use ElementTableWrapper functionality for preloading edge properties
Add cacheAllProperties utility method
Refactoring property parsing to separate method in anticipation of vertex/edge-specific entry parsing