Dynamic plugin configuration

[Enet4]

As part of what we had in mind during the development of our Lucene plugin, we lack the means of reconfiguring a plugin while Dicoogle is running. I propose that we expose this feature with a web service and internally via the SDK. Something like this:

Getting: GET /management/settings/plugin/<plugin-name> : would return an XML document

Setting: POST/PUT /management/settings/plugin/<plugin-name> : I'm not sure how I'd design this one. Providing a full XML document in the HTTP body is impractical because the user might only need to redefine one property. On the other hand, defining an XML element is more than just a key-value pair.

ConfigurationHolder DicooglePlatformInterface#getPluginSettings(String pluginName);
// not sure about this one either
DicooglePlatformInterface#setPluginSettings(String pluginName, ConfigurationHolder config);

Let us use this issue to make a decision on the API.