Renamed property 'agwaBaseUrl' to 'agwaUrl'

_NationalLibraryOfAustralia_WebArchive changes:

Replaced property 'agwaBaseUrl' throughout Javascript code with
'agwaUrl' and replaced config property 'agwa.url.base' with
'agwa.url'. Removed 'agwa.host', 'agwa.port' and 'agwa.path'.

This makes the configuration of agwa-wayback more consistent with
configuration of AGWA. Both have a 'agwa.url' config option which
should contain the same URL.

Newly derived property agwaOriginUrl is calculated from agwaUrl
in setAgwaUrl() and contains just the protocol, host and port,
e.g. http://agwahost:8080. This is used by the postMessage()
function.