Doc updates for plugins_v1.1.
Document common error messages when developing plugins.
Add docs for dependencies.
some copy fixes
move around tools docs and add skeleton for Toolkit
toolkit screenshots and docs
Merge branch 'an_updates'
Merge branch 'master' of github.com:trigger-corp/Forge-Documentation
Merge branch 'feature/plugins_v1.1'
Merge branch 'feature/projects'
Merge branch 'master' into v1.4