Implementation of nested fragments

[cboelter]

Hi,

as discussed I have updated your implementation for nested fragments. I have done the following changes:

• Split the template logic for frontend and backend in two separate templates
• Change the originale template as it has not worked properly with the grid separator logic
• Added a listener to show the grid_parent field in separators only if there is the old start / stop used
• Changed the parent retrivial for the separator
• Added an optional migration to migrate all start / stop elements to the new wrappers
• Synced develop with master

[dmolineus]

I updated the develop branch containing the changes of the master branch and got phpcs working again. Could you rebase your changes on the latest develop branch please?

[cboelter]

@dmolineus hopefully rebased correctly 😨 I've tried to run phpcq after rebase, but I always get the following error:
COMMAND: php vendor/bin/phpcq exec phpcs
ERROR: Referenced sniff "Doctrine" does not exist.

[dmolineus]

The rebase doesn't seem to be correct (too many commits already being part of develop being listed as commits). Therefore I created a rebased version #74 as ongoing pull request.

You should use php vendor/bin/phpcq run phpcs. The doctrine coding standard hast du be injected into the phpcs configuration. That does not work when calling exec.