Concurrent insertion & deletion test
Add insert(key, value) function to clsm

The other queues don't have this yet because it was unnecessary
for our benchmarking purposes, but let's add it here.
Initial item class version
Adapt all CLSM components to <K, V> template
Add item allocator, head, tail to clsm_local
Add next/prev pointers to block
Remove the sequential LSM from clsm_local

This breaks all of our tests (obviously).
Make next/prev block pointers public
Implement the CLSM insert operation