Search functions in external plugins need a restart to work

[yyoyo]

Since 0.5.27, yes.fm is an external plugin.
The 0.5.27 does not contain the yes.fm plugin. it's installed from the repository at first boot as a recommended plugin.

When it's installed, a reboot is needed in order to have yes.fm search engine part working.

Step to reproduce:
1. remove the .moovida/plugins directory
2. Launch Moovida
3. Go in "Available Plugins"
4. install the yesfm plugin
5. wait until yes.fm egg is downloaded
6. go to music => search and search for ABBA

Expected result:
The yes.fm plugin should return some items available

current result:
Yes.fm does not return any results. we have to restart Elisa in order to have a working search engine.

[Philippe Normand (philn)]

The bug is in the "search meta resource_provider". It loads its searchers at initialize time so if a plugin is enabled *after* moovida startup, the resource_provider won't know about it.

The proposed fix is to monitor the message bus for the PluginStatusMessage and when a plugin is enabled: load its searchers (if it has the searchers entry point in its egg-info). When a plugin is disabled, cleanup its searcher(s) if it has any. The meta_resource provider should also be notified at moovida startup (ComponentsLoadedMessage) and scan all the enabled plugins at that moment.