Catalog timeouts mismatched with CVMFS default

[olifre]

As of:
942b207
catalog timeouts are now set to 30 s.
However, checking upstream code:
https://github.com/cvmfs/cvmfs/blob/bfceb7b8fa4a98e27c0409fffe33987e42642478/cvmfs/server/cvmfs_server_apache.sh#L279
and also what a fresh install creates, I see:

    # 60 seconds and below is not cached at all by Squid default settings
    ExpiresByType application/x-cvmfs "access plus 61 seconds"
    ExpiresByType application/json    "access plus 61 seconds"

so this new default of 30 s seems to mismatch upstream and be a bad idea for default squid configurations.

[traylenator]

At the very least we make it a configuration with default. I think 30 may have been introduced locally here.

[traylenator]

@olifre how does #82 look to you?

[olifre]

@traylenator This looks very good, especially to have it configurable!
Many thanks! 👍