Add annotations for data sources and sinks and further static analysis

[emkll]

Pyre [0] allows for further static analysis to ensure untrusted and/or unsanitized input never makes it it's way through to sensitive functions.

We should add annotations for sources, sanitizers and sinks across the codebase in order for this static analysis to run.

[0] : https://pyre-check.org/docs/static-analysis-post-processor.html