Remove xml-apis and xerces dependencies

[berezovskyi]

Description

Remove xml-apis and xerces dependencies from everywhere except for the legacy OSLC Client. Rationale:

• https://stackoverflow.com/questions/11677572/dealing-with-xerces-hell-in-java-maven
• https://www.odi.ch/weblog/posting.php?posting=689
• XML classpath conflict oslc-op/refimpl#2

If your project experiences errors after upsteam removal from our side, you can add the following dependencies to your project (needed ONLY IF you are using ancient APIs from Java 5 times or earlier):

<dependency>
    <groupId>xml-apis</groupId>
    <artifactId>xml-apis</artifactId>
    <version>1.3.04</version>
</dependency>
<dependency>
    <groupId>xerces</groupId>
    <artifactId>xercesImpl</artifactId>
    <version>2.12.0</version>
</dependency>

Checklist

• This PR adds an entry to the CHANGELOG. See https://keepachangelog.com/en/1.0.0/ for instructions. Minor edits are exempt.
• This PR was tested on at least one Lyo OSLC server or adds unit/integration tests.
• This PR does NOT break the API

Issues

Closes #121

[berezovskyi]

I think this needs more testing, will leave it out of the 4.1 release.