Clusterfuzz

- Various bug fixes.

- Added platform support for Fuchsia OS.
- Migrated libFuzzer to the new pluggable engine pipeline.
- Stack parsing improvements.
- Various bug fixes.

- Fixed XSS in login page.

- Added Golang stack parsing.
- Added Sanitizer options minimization.
- Added HELP_FORMAT for custom crash reproduction instructions.
See documentation [here](configs/test/project.yamlL99).
- Added feature to show reproducible variants for a crash on other jobs
(`Reproducer` column in `Testcase analysis on other jobs` section).
- Refactored engine fuzzer code for easy pluggability.
- Reproduce tool improvements - performance fixes, added android support.
- UI improvements - search filter in dropdowns.
- Various bug fixes.

- Implemented issue tracker policy and finishing the refactoring for supporting
different issue trackers.
- Disabled external mutators (Radamsa and ML RNN) for fuzz targets built with
libprotobuf-mutator library.
- Added support for auxiliary fuzzing builds (e.g. DFSan instrumented builds for
libFuzzer).
- Refactored `build_manager` and `fuzz_task`.
- Optimized performance of the most frequently used pages (Testcases and
Testcase Details).
- Added explicit schema for the BigQuery import calls (used to load the fuzzer
stats data into BigQuery).
- Added experimental implementation of the Multi-Armed Bandit algorithm for
fuzzing strategy selection.
- Implemented `variant` task that runs testcases on different jobs in order to
provide more information about the bugs.
- Implemented the new version of the reproduce tool, which currently works on
Linux.
- Various bug fixes.

- Fixed security severity listbox not working.
- More Python 2->3 conversions using futurize.
- Delete button on jobs page.
- New interface for issue management, as part of refactor to support more issue
trackers.
- Android code refactoring.
- Various bug fixes.