control case of package name and its dependencies

Added the following two flags:
  --[no-]python-downcase-name
  (python only) Should the target package name be in lowercase? (default: true)
  --[no-]python-downcase-dependencies
  (python only) Should the package dependencies be in lowercase? (default: true)

fixes #326
Merge pull request #327 from jaybuff/python-downcase

control case of package name and its dependencies