Pre-Load table into GPU memory

[philass]

Currently we Load the data from tables into the futhark context only after processing a query. This may be inefficient if loading this table into context is a lot more expensive than loading the columns to be selected and other things.

This needs to be tested to see if their are performance improvements if the implementation is changed to address the problem with these considerations in mind.

Files that need to be changed in this case

• CLI.cpp
• db_gpu_load.cpp