smb: install smb as both smb:// and cifs://

Summary:
the latter while not IANA registered is apparently used in places. to
cheaply support it we now configure the protocol file for both protocol
'smb' and 'cifs' and installing two protocol files. they are still both
backed by the same plugin and otherwise the same.
code-wise this also required adjustments to the URL validation tech as
it has hardcoded checks for smb schemes.

FIXED-IN: 19.12.3
BUG: 327295

Test Plan:
- cifs://host/share
- cifs://host
- cifs://

all open correctly. they do get translated to smb because of the checkUrl code.

checkUrl seems entirely pointless, SMBUrl does a bit of validation/fixing as part of
updateCache. It occurs to me checkUrl should simply be incorporated into SMBUrl
and we should construct an SMBUrl where we previously called checkUrl. before doing
anything of value we construct SMBUrls anyway, so the isolated logic does absolutely
nothing SMBUrl couldn't do just as well. also needs a unit test -.- ... too much
refactoring for a bugfix though

Reviewers: dfaure, ngraham

Reviewed By: ngraham

Subscribers: meven, feverfew, kde-frameworks-devel, kfm-devel

Tags: #dolphin, #frameworks

Differential Revision: https://phabricator.kde.org/D27291