closes https://github.com/TryGhost/Team/issues/485
In order to loop over all posts, we currently need to pass a visibility="all" flag to a foreach as default for all items in current `visibility` helper is set to `public`. For a post, this behaviour is unintuitive, and inconsistent with the API. Instead, the default visibility should be "all" for the posts. The update allows themes to get all posts directly without passing in visibility -
```
{{#get "posts"}}
{{#foreach posts}}
//Loops over all posts, not just `public`
{{/foreach}}
{{/get}}
```
- The proxy is not a helper, we want the helpers folder to only include helpers
- The proxy is also meant to be the interface to Ghost for the helpers, and we want to enforce that
- This is a small step on the way
refs #10790
- Moved /core/apps into core/frontend
- Moved /core/server/helpers to /core/frontend/helpers along with /core/server/services/themes
- Changed helper location in overrides
- Moved /core/server/services/routing to /core/frontend/services
- Moved /core/server/services/url to /core/frontend/services
- Moved /core/server/data/meta to /core/frontend/meta
- Moved /core/server/services/rss to /core/frontend/services
- Moved /core/server/data/xml to /core/frontend/services
