Read the metadata __Files__ for macros from git and install or remove
files listed there.
__Files__ must be a comma-separated list of files to be copied alongside
the macro. Their path must be relative to the macro (*.FCMacro file)
and not to othe root of the repository. Each file can be prefixed with a
subdirectory.
Separate the Macro class of the AddonManager into addonmanager_macro.py
to prepare for future support for dependent files for macros from the
git repository.
