TS-1827 use HOST as default bucket, not first segment

Original code use the first segment of HOST as the default bucket and
it's not that expandable (two different combo domain may have same
leading segment). Moreover, the initial default bucket("l") will not
be used, because all requests should have a HOST.
TS-1827 allow sub-file's path to contain querystring

i.e. question mark("?") is part of the file path, not the delimiter
TS-1827 request hangs when combo url has no querystring
TS-1827 limit sub-file's max count and querystring's length for potential problems
TS-1827 make plugin per-remap enabled/disabled

add remap code and make global part "intercepted" in
TS_EVENT_HTTP_OS_DNS instead of TS_EVENT_HTTP_READ_REQUEST_HDR in order
to read the flag set in TSRemapDoRemap.
TS-1827 update combo README