analyze and update sonarqube version requirements

[hohwille]

With #5 we entered the SonarQube marketplace and created this configuration:
https://github.com/SonarSource/sonar-update-center-properties/blob/master/devon4j.properties

Some projects are using an older version of SonarQube and cannot use our plugin.
Analysis of this plugin and its history gave me the impression that we rather accidentally came to the minimum SonarQube version 7.9.
Instead we should test and analyze which version of our plugin is working with which version of SonarQube.
If I am correct and we already support lower versions than 7.9, we should update the marketplace entry even for older releases and "fix" this.

[hohwille]

Also this looks like a promising hint to me:

sonar-devon4j-plugin/pom.xml

Line 145 in 5413bf9

<sonarQubeMinVersion>5.6</sonarQubeMinVersion> <!-- allow to depend on API 6.x but run on LTS -->

[hohwille]

So for the analysis of this task someone should do this for several SonarQube versions (e.g. 5.6):

• install SonarQube locally
• install required plugins via marketplace (see documentation)
• install sonar-devon4j-plugin manually by putting the JAR file into extensions plugins folder (not working via marketplace for SQ before 7.9)
• start SQ
• do an analysis of some java project - I would recommend MTSJ and run sonar:sonar on it after successful install build with maven.

If this already works fine with 5.6 we can lower minimum version from 7.9 to that version already. Otherwise we need to test other versions in between that range since we found the real minimum version.

[hohwille]

Time has passed meanwhile and nobody took action here.
IMHO versions like SonarQube 5.x can be considered obsolete/dead/unsupported.
We could easier raise the sonarQubeMinVersion property and go forward.