Fix on default memory

When memory is inputted with --max-memory, UPIMAPI assumes it comes as Gb.

Default in UPIMAPI (when not explicitly inputting) was cheking for available memory, which comes in bytes. This lead to values in memory too large, that lead to values of block-size too small, and the reference database would be split in too many blocks. Then, UPIMAPI/DIAMOND would take forever.

Now, UPIMAPI parses default memory to Gb before determining block-size and number-of-chunks.