Add way to easily customize LAMP application

stack/lamp/apache/instance-apache-php.cfg.in

@@ -13,6 +13,7 @@ parts =
   frontend-promise
   content-promise
   publish-connection-informations
+  ${custom-application-deployment:part-list}
 
 eggs-directory = ${buildout:eggs-directory}
 develop-eggs-directory = ${buildout:develop-eggs-directory}

stack/lamp/buildout.cfg

@@ -74,7 +74,7 @@ mode = 0644
 recipe = slapos.recipe.template
 url = ${:_profile_base_location_}/apache/instance-apache-php.cfg.in
 output = ${buildout:directory}/instance-apache-php.cfg
-md5sum = af0d52de4c10d5a3a64f7c92283ad959
+md5sum = 52627c71c483fe836309f5f430fc0333
 mode = 0644
 
 [instance-apache-import]
@@ -145,7 +145,19 @@ location =
 [application-configuration]
 location =
 
-#----------------
+
+[custom-application-deployment]
+# Optional part allowing applications using this stack to run a custom
+# instance.cfg at the end of Apache/PHP instance deployment.
+# To use it in your application, just override those two parameters, like:
+# path = /path/to/instance-custom.cfg
+# part-list =
+#  part1
+#  part2
+# See software/tt-rss/software.cfg for an example.
+path =
+part-list =
+
 
 [eggs]
 recipe = zc.recipe.egg