fix #1508 -- use real URLs in tag clouds

Signed-off-by: Chris Warrick <kwpolska@gmail.com>
Initial commit to use ghp-import in github_deploy.

The tool automatically rebases before each time it pushes.  We will need
to remove a config variable that currently makes this optional.
Remove unused imports.
Remove the GITHUB_PULL_BEFORE_COMMIT option.

ghp-import always tries to rebase before commits.
Don't set unnecessary attributes on CommandGitHubDeploy.

Minor refactor.
Set default values for github deploy config variables.