[Dicson] use manifest.ini files in plugins to have a separate file for plugin's information. Fixes #5920

Also use sed to remove now unneeded Vim lines, 2to3 -f ws_comma to fix
some whitespace, and fix some other madness manually.

Fixed log_calls decorator arguments in a few plugins. Fixed Acronyms Expander plugin (not working due to bad auto-merge). Added few comments.

Three core (raw) events (iq, message, presence) go also through Network Events Controller (layer between network library and Global Events Dispatcher, newly added) and from there they are dispatched through Global Events Dispatcher.
Ability to register new incoming network events (based on exisiting one) added. Modify-only network events are possible (eg. add some text each message, but don't create any new global event). Events creation can be chained.
Examples of new network events classes are in New Events Example plugin.
Events from src/gajim.py now all go through Global Events Dispatcher and only through it (easy to modify, in chain, data passed with them).

Snarl Notifications plugin initial version added. New events (from current core) go also through GED.