plugins/script: remove 'user'
resources/mark2.default.properties: remove plugin.script.user
resources/mark2.default.properties: fix plugin.trigger.filename

(it's really called plugin.trigger.path)
manager: don't load disabled services
services/user_server: behave better if the service gets reloaded.

It's still a very bad idea to reload services, but the results if you
do will now be slightly less bad.
plugins: use a dict instead of list for the default load/save_state
plugins: minor cleanup
properties: fix Mark2Properties.get_service
plugins/irc: put "irc: " in front of the "failed to log in" message
plugins: convert errors during initialization into PluginLoadErrors.

(so they're reported correctly instead of being propagated up and
breaking stuff)
plugins/rss: fix 're' import