HPCC-10583 Make new ECL Watch the default

Made EclWatch show up in the root page http://IP:port.

Should also work from the old url:
http://IP:port/esp/files/stub.htm?Widget=HPCCPlatformWidget

Legacy can be accessed from http://IP:port/?legacy

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
HPCC-10583 Custom root page should use httpContentFromFile

This will use common routine for setting cache headers, Content-Type,
etc.

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>