Added parameter for the sole usage of the z-.. CSS classes

Instead of enabling the compat_layer for the legacy css this config parameter allows to only enable the legacy css styling. All the other slowdown, memory consuming parts can be left out in that way.
Updated the action buttons in the Extensions modulelist

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | -
| Refs tickets  | -
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Added color parameter and updated the .png images that did not work any more. It adds a little color to the module list and makes sure that module plugins have an icon again (like scribite for instance). I used paperclip for that.
[Imagine plugin] Changed outset into outbound in plugin

Q | A
------------- | ---
Bug fix? | no
New feature? | no
BC breaks? | no
Deprecations? | no
Tests pass? | -
Fixed tickets |
Refs tickets | https://github.com/zikula/core/commit/cc9c57b02cb21b147565d9f70379f1cec9b744da
License | MIT
Doc PR | -

In the Imagine plugin now also everywhere outbound is being used for THUMBNAIL_OUTBOUND mode instead of outset.
We have inset and outbound now.