Pluginize reports view

This patch makes reports view optional instead of mandatory. User can
switch on and off this view and have more space on views pane.
Developers will benefit by saving on build time of this plugin.

This patch introduces kmm_menus shared library for QActions to work
seamlessly across plugin interface. It's worth considering merge with
settings and icons in the future, as these libraries are often required
together.

Differential Revision: https://phabricator.kde.org/D11833