Slightly simplified the unified view change

I removed the storage level table property setting (and instead, always hard code this to MEMORY_AND_DISK for now).

To finish off this change set, let's remove the reference to "unify", and rely on a table property called "shark.store" (or "shark.cache"), which can have the following value: memory, memory_only, tachyon, default (which is just normal Hive tables). 

Let's also get rid of the reload on restart property, and simply reload all memory tables automatically (but do provide a command line option to disable the loading altogether).