Rename members directory -> projects directory.

As part of the transition to have the canonical URL for member projects
be "projects" instead of "members", rename the directories.

The following rewrite rule will be needed in Apache configuration now:
RewriteRule ^/?members?/index.html$ supporter/ [L, R]
RewriteRule ^/?members?/(.+)$ projects/$1 [L, R]
RewriteRule ^/?members?/?$ supporter/ [L, R]