Downgrade CaskAlreadyInstalledError to a warning

Automatic installs - like thoughtbot's laptop script - fail when we
use Homebrew's onoe method.  Using opoo (to warn) will let the
scripts complete successfully when they try to install packages that
have already been installed.

Test for downgrading AlreadyInstalledError to warning
better handling for invalid `url` stanzas
chg `checklinks` to internal command `_checklinks`

* `checklinks` is a very simple implementation useful only for development purposes
* it has no test coverage, only one line of documentation
* users regularly experiment with it and break it, especially
 `brew cask checklinks` with no arguments, which tests all Tapped Casks
improve error message in `brew cask _dump`
update navicat-premium to version 11.1.5

* re-use version number
* update licence
re-use version + license in navicat-data-modeler
update navicat-for-mariadb to 11.1.5

* reuse version
* set license
update navicat-for-mysql to 11.1.5

* reuse version
* set license
update navicat-for-oracle to 11.1.5

* reuse version
* set license
update navicat-for-postgresql to 11.1.5

* reuse version
* set license
update navicat-for-sql-server to 11.1.5

* reuse version
* set license
update navicat-for-sqlite to 11.1.5

* reuse version
* set license
re-use version in bathyscaphe
re-use version in colorpicker-rcwebcolorpicker
re-use version in fourk-youtube-to-mp3
re-use version in graphsketcher
re-use version in pandora-one
re-use version in powerword
re-use version in razer-synapse
re-use version in trailer