Implement auto-saving on Content Types grid
Fix broken processor actions on Import screens
Fix autosave grid action for media sources, remove unneeded autosave parameter on types grid
Support PHP use statements in Snippets and Plugins

This provides a more long-term solution for and closes #557
Implement auto-save on Content Types grid

Merge remote-tracking branch 'origin/pr/705' into develop

* origin/pr/705:
  Implement auto-saving on Content Types grid
Fix broken processor actions on Import screens

Merge remote-tracking branch 'origin/pr/707' into develop

* origin/pr/707:
  Fix broken processor actions on Import screens
Fix autosave grid action for media sources

Merge remote-tracking branch 'origin/pr/708' into develop

* origin/pr/708:
  Fix autosave grid action for media sources, remove unneeded autosave parameter on types grid