Make Travis CI more copy-able to plugins

[janpio]

This rewrite the travis CI config in a way so that it can almost just be copied over to the plugin repos (besides the Sauce Key in addons.jwt.secure). This should make updating the config in the plugins much easier and more efficient.

• Extract PARAMEDIC_BUILDNAME to before_script to make it more obvious this is a variable
• run npm run eslint (and fix file that was not passing that check)
• run npm install -g github:apache/cordova-paramedic if not running in paramedic repo
• Create TEST_COMMAND, PARAMEDIC_PLUGIN_TO_TEST and PARAMEDIC_COMMAND that are filled depending on what repo the config is run for (paramedic vs. plugin)
• simplify syntax

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@alsorokin This changes the format of the buildname on Saucelabs from travis-plugin-splashscreen-383.8 to travis-apache/cordova-plugin-splashscreen-383.8. Any reason why this might be bad idea?

[alsorokin]

Any reason why this might be bad idea?

Everything should be cool 😎