Add v10 support, drop TYPO3 v8 support

[djcprinse]

I've rewritten the ext_localconf.php to make it work with v10 again. Since v10 dropped the $_EXTCONF variable outside the ext_emconf.php declaration file, the ExtensionConfiguration class should be used to get extension configuration. v9 also supports this way of getting extension configuration. This made me decide to drop support for TYPO3 v8.

I've updated the composer.json to include TYPO3 v10 versions and removed support for v8 because. I've also cleaned up the ext_emconf declaration file by removing deprecated options. I've updated the requirements and dependencies and removed the php dependency since TYPO3 v9 requires a minimum of php 7.2

Since the extension did not yet have an icon, I've added the New relic logo as extension icon. And I've removed the composer.lock since it shouldn't be shipped with the extension I think. Another approach could be to add it to the .gitattributes if you believe this file is necessary.

Feel free to give feedback if you don't agree with some approaches. I've never published an extension through to TER, so I don't know if the adjustments to the declaration file are useful. Also the version number should be changed if a new release is published.

[djcprinse]

Closing this pull request because version 1.3.0 has been release and contains TYPO3 v10 support

[NamelessCoder]

I decided to go with the other PR since that preserves 8.7 compatibility - hopefully it serves your purposes! ;)

[djcprinse]

Sure, no problem!