SES-845: Use the current Tomcat Maven plugin, and Tomcat 7.

The Tomcat Maven plugin has moved to Apache. Use the new artifact,
in its Tomcat 7 flavour.
SES-845: Match the welcome document for filtering.

Tomcat bug 49914 indicates that their interpretation of the spec is
that the welcome file mapping is applied before any filters are
matched. Add another pattern, so that both cases will qualify for
URL rewriting and Tomcat will also redirect.
SES-845: Tell Tomcat to track sessions only with cookies and not URL rewriting.

Add a setting to track sessions only with cookies, and not by
rewriting URLs to include ';jsessionid='. This looks ugly in browsers.
This syntax also breaks Group.getViewByName's assumptions about URLs,
as it looks up by path and doesn't ignore matrix parameters.
Merged in jwalton/sesame/SES-845-initial-redirection (pull request #313)

SES-845: Fix redirection for welcome page in Tomcat 7