LicenseListParser: Fix parsing of nested expr'ns
LicenseListParser: Fix parsing of nested expr'ns

Nested license expressions were not correctly parsed by the previous
grammar, and the operator precedence AND > OR was also not handled
correctly. Fix this by refactoring the license parser.

Signed-off-by: Clemens Lang <3a6d3609d3aad392a589e22c59fac9e2a5d6c77d@bmw-carit.de>

spdx/tools-python