Refine warm_start behavior with template option

[weixuanfu]

1. warm_start now saves both Primitive Sets and evaluated_pipelines_ from previous runs (issue Warm start: Population doesn't persist when running for max_time_mins #946 Follow up to issue #892 #980 )
2. fix a bug that TPOT assign bad fitness scores to non-evaluated pipelines (interrupted by max_min_mins or KeyboardInterrupt) (issue Warm start: Population doesn't persist when running for max_time_mins #946)
3. saving primitive sets when template is not default fix the bug that mutation operator cannot generate new pipeline (issue Evaluated pipelines not containing all models #982)

[coveralls]

Coverage increased (+0.06%) to 96.747% when pulling 9b8355f on weixuanfu:issue_981 into 99ec8f8 on EpistasisLab:development.