Fix __all__ mypy warnings

[thopre]

Summary

mypy warns about the unknown type for empty all. This commit adds
type info for them. Import errors for typing module in LNT needs to be
ignored because LNT module is imported from setup before all required
package are guaranteed to be installed.

[PrzemekWirkus]

LGTM

lnt/__init__.py

 __author__ = 'Daniel Dunbar'
 __email__ = '[e-mail]'
 __versioninfo__ = (0, 4, 2)
 __version__ = '.'.join(map(str, __versioninfo__)) + '.dev0'
 
-__all__ = []
+# lnt module is imported from the setup script before modules are installed so
+# modules might not be available.
+try:
+    from typing import Sequence
+except Exception:
+    pass
+
+__all__ = [] # type: Sequence[str]

lnt/external/__init__.py

-__all__ = []
+from typing import Sequence
+
+__all__ = [] # type: Sequence[str]

lnt/server/__init__.py

-__all__ = []
+from typing import Sequence
+
+__all__ = [] # type: Sequence[str]

lnt/server/db/__init__.py

-__all__ = []
+from typing import Sequence
+
+__all__ = [] # type: Sequence[str]

lnt/server/db/rules/__init__.py

-__all__ = []
+from typing import Sequence
+
+__all__ = [] # type: Sequence[str]

lnt/server/reporting/__init__.py

-__all__ = []
+from typing import Sequence
+
+__all__ = [] # type: Sequence[str]

lnt/server/ui/__init__.py

-__all__ = []
+from typing import Sequence
+
+__all__ = [] # type: Sequence[str]

lnt/testing/util/__init__.py

 """
 Miscellaneous utilities for generating test data.
 """
 
-__all__ = []
+from typing import Sequence
+
+__all__ = [] # type: Sequence[str]

lnt/util/__init__.py

 import logging
+from typing import Sequence
 
 logger = logging.getLogger("lnt.server.ui.app")
 
-__all__ = []
+__all__ = [] # type: Sequence[str]