Summary:
* add run_pokec script because more than one step is required
* refactor of plot_throughput script
* move all plot scripts under tools/plot
Reviewers: mferencevic, teon.banek, mislav.bradac
Reviewed By: mferencevic
Subscribers: florijan, pullbot, buda
Differential Revision: https://phabricator.memgraph.io/D1106
