Lock GVL files to avoid multiple file creation/deletion in multi-job settings

[d-laub]

For example, when running GVL using the same reference genome file with parallel jobs, the GVL file created for the reference can be corrupted since each job tries to create the file at the same time. Adding file locks to all instances of GVL file reading and creation should fix this. For implementation, a starting place may be the write/init funcs of each class that corresponds to a file.