[META] phpList core phase 2

[oliverklee]

This meta ticket covers the core-related tasks for phase 2. The base-distribution-specific tasks are listed in phpList/base-distribution#18, the rest-api-specific tasks are listed in phpList/rest-api#20, and the web-frontend-specific tasks are listed in phpList/web-frontend#16.

• #131 get the Travis builds to work on Trusty
• #133, #138 rename the branch alias from 4.0.0-dev to 4.0.x-dev https://getcomposer.org/doc/articles/aliases.md#branch-alias
• #135 add a .htaccess
• #136 add the Symfony console
• #139, #140 automatically determine the application root directory
• debug logged routing exception (was the 404 error for the missing favicon)
• #141 move the bin/ and web/ dir copying script to the core
• #122 add favicons in different sizes (to avoid the 404 errors)
• #145 fix error "You are not allowed to access this file." in development mode
• #146 set up the log and cache directories
• #148 move the environments to an interface
• #134, #137, #147, #149 make the project structure more similar to the default Symfony project structure
• #147, #149 clean up the configuration files
• #150 add a server console command and document it
• #150 document how to use the different environments
• de-duplicate the director creation in the repositories
• add a structure for a configuration file that is outside the vendor folder
• #175 rename Bootstrap::preventProductionEnvironment
• #151, #153, #158, #168 add a mechanism for modules to register themselves to the core via Composer
• #168 document how to create/add modules
• #168 remove the dependency on the REST bundle
• #181 automatically clear and warm all caches on composer update
• #182 document when to use the REST API and the repositories when writing modules
• #180 configure the "hello world" route to only accept GET requests
• #183 rename the "hello world" route
• #183 make the root route an official "nothing is here yet" route
• #183 rename ApplicationBundle to HelloWorld bundle
• move the CI stuff into a shell script (or into several scripts)
• #188, #189 move the production secret to environment variables or the "outside" configuration file
• #190 add DB configuration via YAML files
• #196 use the Symfony-Doctrine integration
• #179, #205, #207 add DI and use it
• #203 Allow modules to provide their own (non-service) configuration
• #218 add a model and repository for lists
• use the FOSRestBundle for rest-api
• #223 add a model and repository for subscribers
• allow setting the DB configuration via a configuration file in addition to environment variables
• have a look at other systems and their APIs
• #194, #235 Fix cache clearing for broken configurations