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Add support for LDAP manager and search

New configuration settings have been implemented to allow additional
LDAP environments:
* `security.ldap.user-search-filter`
* `security.ldap.user-search-base`
* `security.ldap.manager-user-dn`
* `security.ldap.manager-password`

See merge request !12

An LDAP search pattern can now be used instead of binding with a DN
pattern.

This reverts commit fc78eb18.

SASS variables only exist at compile time and are not available for
arsnova.properties.

Paul-Christian Volkmer authored 9 years ago and Daniel Gerhardt committed 9 years ago

See http://platform.spring.io/platform/ for more information about it.

This patch makes Spring.IO usable with ARSnova Backend and also updates
some dependiencies not beeing upgraded in ARSnova Backend POM
so I removed explicit version declaration.

Problems with json-path-assert dit not occure, so i removed version
declaration and use managed version 2.0.0.

Remove obsolete version properties

Closes GH-17. This is a squshed version of PCV's PR. (DG)

Swagger api

new descriptions for the swagger api doc in the entity-classes

See merge request !11

Add a default exception handler to catch non handled exceptions

The default exception handles all excaptions not handled by the
following handle methods.

It creates a response, containing the HTTP status description
and the exception message.
This response can be serialized into JSON.

It generally might not occure but in some conditions the previous code
could be used to inject something into response by manipulating the
origin header to include some \n or \r.
These sequences should not occure in results CORS headers.

Patch replaces all \n or \r in origin header with a white space char.
Newer servlet containers like Tomcat 7.x fix this problem, but it might
be a good idea to fix this issue within ARSnova.

See: https://www.owasp.org/index.php/HTTP_Response_Splitting

NovaEvents is derived from ApplicationEvent which extends EventObject.
EventObject implements Serializable.

It is bad practice if defined instance fields within NovaEvents
derived classes do not implement Serializable.

A boxed primitive is created from a String in
* RangeAspect#handlePaginationRange()
* LoginController#dialog()
just to extract the unboxed primitive value with Integer#valueOf().
This creates an Integer object. It is more efficient to use parseInt()
which creates a primitive int.

Corrected random indention in LoginController

In getSkillQuestion() a call to stubQuestions.get() contained an argument
with an incompatible class. Session will be converted into String using
toString() but this is not what was intended to do here.

In saveQuestion() the CouchDB document ID was used, but the sessions
keyword should have been used instead.

User object will be serialized into a String using toString() but this
should not be done in a unit test.

Interactive API documentation

Supersedes !5.

> This feature supports developers with an interactive documentation of
> the REST API from the ARSnova Backend.

Changes & Todos:
* Branch & code clean up
  * Rebase on master
  * Squash related commits authored by the same developer
  * Remove commits whose code has been reverted later on
  * Fix whitespaces
* Remove implementation notes (Java signatures are not helpful)
* Improve documentation of responses (Tom Käsler)
  * Do not define status messages for methods individually (DRY)
* Create JSON at compile-time by using
  [swagger-maven-plugin](https://github.com/kongchen/swagger-maven-plugin) (Tom Käsler)

See merge request !10