Rename "supporter" to "sustainer" in templates and URLs.

Does not rename the models.

Substantial update of Member Project Application page.

This page had much out of date material, particularly the timeline
and the types of projects we seek, but also the FAQ section did not
include standard information that we're now regularly giving projects
during intake.

This update attempts to address many of those issues.

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]