Make extension compatible for TYPO3 v8
<p>I have a problem in TYPO3 v8.5.0 dev with own extensions.
After creating a proper composer.json my classes are not found. Installation was done by copy into the typo3conf/ext folder as usual and activating in extension manager. Unfortunally the ext is not in TER, so this is the only way.
After activating, i'm stuck with error:</p>

<blockquote>
  <p>Oops, an error occurred!</p>
  
  <p>Class 'XXX\ExtKey...' not found</p>
</blockquote>

<p>What do I miss so my classes are found again?</p>