Rework plugin structure

[sebinside]

Since the beginning of version 2 of chat overflow, plugins are identified by a pluggable holding all metadata and a plugin class, holding the execution information and requirements.

This should be reworked. Pluggable should not be needed and replaced by a metadata file in the plugin jars resources. The class loader and framework could has to be updated.

[hlxid]

I would like to start working on this, but still have some questions:

1. What file format should be used? Propably xml?
2. Should multiple plugins in one jar be supported? The current code just complains, but allows it:

   chatoverflow/src/main/scala/org/codeoverflow/chatoverflow/framework/helper/PluggableLoader.scala

   Lines 28 to 32 in 2cde2f9

   	pluggableObjects.length match {
   	case 0 => logger warn "No pluggable classes found."
   	case 1 =>
   	case _ => logger warn "More than one pluggable class found."
   	}

3. Should pluggable be directly removed with pre-alpha 3 or be deprecated and slowly removed?

[sebinside]

Some ideas / notes on this:

• keep all pluggable meta data in a required xml file
• rework the PluginFramework to load this xml file (e.g. called plugin.xml) before loading the Plugin file
• only allow one xml and one plugin class per jar
• rework the create task (see issue Enhance plugin create task #20) to automatically create the proposed structure with the given choice for java or scala, already containing a require for e.g. the sample connector to show the usage
• rework the fetch task, to only add a plugin to the plugins.sbt if the plugin xml file exists. Its currently a pain in the ass to delete plugins because of this
• think about other usefull (optional) fields in the xml file, e.g. a support website / source github repo or license. Maybe npm does have other usefull examples
• deprecate all other approaches. this is main reason we still call it pre-alpha

I hope this answers all your questions. Another spontanious idea: the plugin version could be also embeeded into the xml. Minimal sbt file changes, minimal framework reloads...

[sebinside]

Just an idea...

<plugin>
  <name>sampel</name>
  <author>sebinside</author>
  <description>Just a test</description>
  <api>
    <major>3</major>
    <minor>0</minor>
  </api>
  <version>0.4.2</version>
  <website>codeoverflow.org</website>
  <license>MIT</license>
</plugin>