Otherwise, WOPI implementations that use non-standard ports get CSP
voilation errors in the browsers because Poco's URI::getHost() method
strips the port number from the host.

No harm in mentioning the port number always even if its a standard one,
so always use Poco::URI::getPort() to append the port to the frame
ancestor.

Change-Id: I9e7a7021b38f717e14af3d389e30f24ecaf6d122