don't return the spending methods pay_invoice and multi_pay_invoice in
the get_info request and the info event so connections can be used for
services that enforce receive only connections.
- both internal and external plugins require GUI install
(except internal HW plugins, which are 'auto-loaded' and hidden)
- remove init_qt hook
- in Qt, reload wallet windows if plugin enabled/disabled
- add 'uninstall' button to PluginDialog
- add 'add plugins' button to wizard hw screen
- add icons to the plugin list
