Manage dependency of a plugin on an group (parent plugin)

Here are some examples of use cases that we want to cover :

• The Developer Cockpit plugin can't be used without the SCM ecosystem
• The VB.Net plugin can't be executed without the .Net ecosystem
• The SCM Stats plugin can't be used without the SCM ecosystem
• The Clover plugin can't be used without the Java ecosystem

To achieve this, the following new properties must be supported :

• By the Sonar packaging plugin :
  • Plugin-RequiresPlugins: [parentPluginKey1]:[minimalParentPluginVersion1], [parentPluginKey2]:[minimalParentPluginVersion2], ...

The following updates are required in the "Update Center" pages :

• Installed Plugins
  • For a group of plugins having an incoming dependency :
    • Uninstalling this plugin will also uninstall : ...
  • For a group of plugins having an outgoing dependency :
    • Depends upon : ...
• Available Plugins
  • For a group of plugins having an outgoing dependency :
    • Installing this plugin will also install : ...
• Plugin updates
  • For a group of plugins having an outgoing or incoming dependency :
    • Updating this plugin will also update : ...

And when a Sonar server is started, we should fail with a meaningful error message in the following cases :

• A required plugin is missing : "The plugin 'xxx' required by 'yyy' is missing"
• A dependency cycle exists between plugins : "There is a depency cycle between plugins 'xxx', 'yyyy', ... that must be cut"
• A required plugin doesn't have the minimum required version : 'The plugin 'xxxx' is in version x.y.z whereas the plugin 'zzz' requires a least a version y.t'