Filter adjustment when opening context from plugin

Filter adjustment when opening context from plugin

- Clear filter only when a plugin is selected manually.
  Plugin dir should be unfiltered when opened.
- Plugins invoked by keys don't require clearing filter
  of original context. If a new context is opened using
  the plugin, it will be unfiltered by default. If the
  same context is re-used (when all the contexts are in
  use) the filter should be cleared so the the new path
  is opened unfiltered.