Reorganize online PE

This MR reorganizes gwcelery/tasks/inference.py, which was originally written only for LALInference, while it is now being used mainly for Bilby and RapidPE-RIFT. The main changes are to stop uploading a LALInference ini file for every event, and to set up separate tasks to upload results for different pipelines to make it easy to maintain them.

This MR includes the following changes:

• gwcelery/tasks/orchestrator.py and gwcelery/tasks/inference.py: reorganization so that it won't always upload lalinference ini file.
• gwcelery/tasks/inference.py: utilize the event object downloaded at the first stage to reduce the number of downloads
• gwcelery/tasks/inference.py: web directory of PE outputs is changed to app.conf['pe_results_path']/{superevent_id}/{pe_pipeline}
• gwcelery/tasks/inference.py: separate tasks to upload results for different pipelines to make it easy to maintain them
• renaming online_pe.jinja2 to lalinference.jinja2
• fix typos and clean up/add docs
• gwcelery/tests/test_tasks_inference.py: reorganization due to the changes above
• gwcelery/tests/test_tasks_orchestrator.py: add test of parameter_estimation

This should go after !1026 (merged) and !1006 (merged).