Replace the `buffer_pool_slots` command line flag with a more intuitive flag

[pateljm]

The current command line flag, buffer_pool_slots, can be used to set the number of buffer pool slots. A constant in the code sets the slot size to 2MB. A user wanting to specify the buffer pool should simply have to specify something like ``--buffer_pool_size = 10GBand the system should calculate the number of buffer pool slots that don't exceed this limit. A check should also be made to make sure that this setting is "safe" and not greater than the installed memory. For the latter, the methodcalculateTotalMemoryInBytes` can be used.