A mass updates to bring plugins into line with style guidelines:
- Move smallish docstrings to the top-level nodes.
- Removed irrelevant << version history >> sections.
- Moved smallish imports to top-level nodes.
- Move Leo directives to end of top-level nodes.
- Corrected various problems, mostly import-related, reported by pylint.

The diffs look hairy, but close inspection reveals that most changed lines are blank or comment lines.
Pylint passes for all files.  All unit tests pass, but there is a small possibility that some changes may cause problems.

Leo build: 20140918084342