[plugin, mail] remove plugins thunderbird and outlook

removed following modules
1) plugin
2)plugin_thinderbird
3)plugin_outlook

Task :- https://openerp.my.openerp.com/web#id=7834&view_type=form&model=project.task&action=327
Pad :-  https://pad.odoo.com/p/r.uxX1rLbeuqKeMv76