[Security] Split the component into 3 sub-components Core, ACL, HTTP
[Security] [SimpleAuthenticationProvider] Delete unnecessary "use" statements
[Security] copied the Resources/ directory to Core/Resources/
[Security] fixed README files
[Config] Create XML Reference Dumper
merged branch WouterJ/dump_xml (PR #8635)

This PR was squashed before being merged into the master branch (closes #8635).

Discussion
----------

[Config] Create XML Reference Dumper

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

Only Yaml was supported. This PR adds support for XML. This makes it easier to test XML schema's (see symfony-cmf/MenuBundle#114 ), helps us at the docs with our configuration reference and helps others using XML with symfony.

## Todo

 - [x] Prototyped arrays don't work properly
 - [x] Add comments (see Yaml dumper)
 - [x] Add namespaces support

## Side effects

I've moved the reference dumpers to their own namespace and renamed the original reference dumper to `YamlReferenceDumper`. The old one is kept for BC, but deprecated.

/cc @dantleech

Commits
-------

05e9ca7 [Config] Create XML Reference Dumper
fixed previous merge (refs #8635)
[Security] removed unneeded hard dependencies in Core
merged branch fabpot/security-split (PR #9064)

This PR was merged into the master branch.

Discussion
----------

[Security] Split the component into 3 sub-components Core, ACL, HTTP

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #9047, #8848
| License       | MIT
| Doc PR        | -

The rationale behind this PR is to be able to use any of the sub components without requiring all the dependencies of the other sub components. Specifically, I'd like to use the core utils for an improved CSRF protection mechanism (#6554).

Commits
-------

14e9f46 [Security] removed unneeded hard dependencies in Core
5dbec8a [Security] fixed README files
62bda79 [Security] copied the Resources/ directory to Core/Resources/
7826781 [Security] Split the component into 3 sub-components Core, ACL, HTTP
merged branch alexpods/patch-4 (PR #9066)

This PR was merged into the master branch.

Discussion
----------

[Security] Delete unnecessary "use" statements

 Delete unnecessary "use" statements in SimpleAuthenticationProvider

Commits
-------

82de3ba [Security] [SimpleAuthenticationProvider] Delete unnecessary "use" statements