Fix #64

[Bitmapped]

This pull request fixes Issue #64 which happens when editor types are defined in package manifests.

Switch to use UmbracoConfig method to load grid editors rather than just reading from grid editors config file. This handles editors coming from manifest files as well.

Also switched to use Umbraco IGridEditorConfig instead of GridEditor class, which I've marked as deprecated. The custom class is redundant.

[soreng]

Hi @Bitmapped LeBlender is build to manange grid.editors.config.js

There is no "source" on an editor, so when/if we use umbracos grid-editor discovery, we get editors from other sources than grid.editors.config.js. Upon editiing a non-grid.editors.config.js
editor, we don't know where to save it.

[Bitmapped]

@soreng I understand what you're saying about editing, but LeBlender does work with using grid editors from packages to pages. Judging by PR #71, I'm not the only one using things this way.

The current solution throws a NullReferenceException and clogs up the logs. That's not a good way forward. Do you want me to just fix things up to eliminate the NullReferenceException or how do you want to handle this? I'd like to get this issue resolved either way with a fix incorporated into the main codebase either way. I'm not too particular.