* Adds support for getting a Lean symbol based on FIGI, CUSIP, ISIN, SEDOL
* Address review: bug fixes for mapping, improve docs, cleanup & refactor
* Make LocalZipMapFileProvider and LocalZipFactorFileProvider only
initialize if they haven't been initialized yet.
* Address review: makes ISIN, SEDOL, CUSIP case-insensitive
* Cleans up map file provider in SecurityDefinitionSymbolResolver
* Modifies some test cases to test for case-insensitivity
* Add null check for SecurityDefinitions
* Fix unit tests
Co-authored-by: Martin-Molinero <martin@quantconnect.com>
Gerardo Salazar
024d416ddd