* Move some code outside dbms/src folder
* Fix paths

Scenarios that use Arena::allocContinue may waste quadratically many
memory and perform quadratically many copying, when the memory range
size reaches Arena's linear allocation threshold. To alleviate this,
make sure that the next memory chunk allocated by allocContinue is at
least linear_growth_threshold bytes bigger than the previous one, so
that we don't reallocate and copy that often.