Update PhpUnitWrapper.php & TestRunner.php to recommend PHPUnit installation via Composer rather than PEAR

Using the PEAR Installer to install PHPUnit is no longer supported.  See https://github.com/sebastianbergmann/phpunit/wiki/End-of-Life-for-PEAR-Installation-Method.

Replace PEAR in a comment and die output message with Composer.

Signed-off-by: AntonyThorpe <antony.thorpe@budget12.com>
Merge pull request #3476 from AntonyThorpe/PEAR-PHPUnit

Update PhpUnitWrapper.php & TestRunner.php to recommend PHPUnit installation via Composer
Adding some README badges for downloads, license and stable version.
Fixing broken docs on setting allowed extensions on a FileField

Refers to an invalid variable, and is overriding the entire Upload,
which isn't necessary.
Merge pull request #3478 from halkyon/readme_badges

Adding some README badges for downloads, license and stable version.
Merge pull request #3480 from halkyon/allowed_exts_doc_change

Fixing broken docs on setting allowed extensions on a FileField
Fix #3356 js not properly included