Instead of explaining how to setup Piwik in multiple places we should always link to the developer zone.

we will deprecate old test classes in 4 months and not in 2, simplified test run by only allowing short version, added some examples

refs #5940 we might stay backwards compatible this way for 2 months. moved some tests from unit to integration and explained when a test is a unit test, an integration test or a system test.

refs #5940 put tests in correct folders, better testsuite names, some tests still fail and I cannot figure out why

Refs #5031 The build is green: https://travis-ci.org/piwik/piwik we're running latest PHPUnit using composer.

Instructions to install PHPUnit, run `php composer.phar update` in the Piwik root directory.

                 Add the PHPUnit binary path to the your PATH environment variable. For example on Linux:
                 Edit `.bashrc` in your home directory and add the following line:

                     export PATH=/path/to/dir:$PATH

                 You will need to source your `.bashrc` or logout/login (or restart the terminal) for the changes to take effect.
                 To source your `.bashrc`, in your home directory simply type

                     $ source .bashrc

                 See [PHPUnit doc](http://www.phpunit.de/manual/current/en/installation.html).

Refs #5031 Now getting PHPUnit from composer/packagist. This will make like better for core team devs
Updating readme with instructions.
I also hope this will solve the Autoloader issue on the UI build: https://travis-ci.org/piwik/piwik-ui-tests

Fixes #4614 Remove VisualPHPUnit from the codebase, since we don't use the tool anymore (everyone using PHPUnit in command line)

clarifying screenshots test setup

Enabling All plugins during tests