[PHP] Add gitignore to AbstractPhpCodegen (#765)

* [PHP] Remove PHP related rules from root gitignore

After conversation with @ackintosh we've agreed that every PHP codegen
should create it's own `.gitignore`. Client libraries(SDKs) should ignore
`composer.lock` file while server stubs better do opposite.

* [PHP] Set .gitignore as default supporting file

* [PHP] Add default gitignore to Client SDK

* [PHP] Add default gitignore to Laravel

* [PHP] Add default gitignore to Lumen

* [PHP] Add default gitignore to Silex

Seems like issue #663 and pull request #681 missed this security script,
I've changed output path in bin/security/silex-petstore-server.sh.

* [PHP] Update Slim

* [PHP] Add default gitignore to Symfony

I've copied few old rules from root gitignore to local one. These rules
should be reviewed by original SymfonyCodegen authors.

* [PHP] Add default gitignore to Zend

* [PHP] Refresh Openapi3 client samples

* [PHP] Add refs to .gitignore templates collection

samples/server/petstore/php-symfony/SymfonyBundle-php/.gitignore

@@ -0,0 +1,54 @@
+# ref: https://github.com/github/gitignore/blob/master/Symfony.gitignore
+
+# Cache and logs (Symfony2)
+/app/cache/*
+/app/logs/*
+!app/cache/.gitkeep
+!app/logs/.gitkeep
+
+# Email spool folder
+/app/spool/*
+
+# Cache, session files and logs (Symfony3)
+/var/cache/*
+/var/logs/*
+/var/sessions/*
+!var/cache/.gitkeep
+!var/logs/.gitkeep
+!var/sessions/.gitkeep
+
+# Parameters
+/app/config/parameters.yml
+/app/config/parameters.ini
+
+# Managed by Composer
+/app/bootstrap.php.cache
+/var/bootstrap.php.cache
+/bin/*
+!bin/console
+!bin/symfony_requirements
+/vendor/
+
+# Assets and user uploads
+/web/bundles/
+/web/uploads/
+
+# PHPUnit
+/app/phpunit.xml
+/phpunit.xml
+
+# Build data
+/build/
+
+# Composer PHAR
+/composer.phar
+
+# Backup entities generated with doctrine:generate:entities command
+**/Entity/*~
+
+# Embedded web-server pid file
+/.web-server-pid
+
+# From root gitignore
+/Tests/cache/
+/Tests/logs/