The standard PluginInstall has a nasty bug which uses the source
path as part of installation path. Remove, and use a simple
OpenCPN.app prefix

The loader expects the apple tarball to have paths like:

  - OpenCPN.app/Contents/PlugIns: .dylib plugin file, binaries
    and helper libs.
  - OpenCPN.app/Contents/Resources: .lproj gettext translations
    directories.

The prefix is discarded and could be anything.

Let "make package" build both the traditional installer and the
new installation tarball. Remove references to other formats,
notably rpm.

Some places including bintray uses a common namespace for all
plugins. Make sure the plugin filename is unique by including
both source and target name and version.

We are using deprecated and finally failing stuff.
See: OpenCPN/OpenCPN#1452

Updating the key is error-prone and requires the secret key. It
also requires the travis command line utility. Using that and
the key I was finally able to update .travis.yml using

travis encrypt -x -a deploy.key -r leamas/squiddio_pi  <my key>

-x: Overwrite existing key
-r: Name of repo

Note that the repo is part of the key so after forking a new,
encrypted key must be generated.

The travis bintray integration seems just unstable. Use a raw
access to the REST API in a shellscript instead.

... and move tarball location to cloudsmith

Installable plugin generation

plugin.xml.in: Fix copy-paste error.

comment out Line 45  make create-dmgg

The ci/control file could and should be updated to work with all Ubuntu
versions applicable. Leaving it in place, to be overwritten in build
process.