EZS-14 - Build "Create Content" module in the sidebar of PlatformUI

Created a sidebar module to allow a user to create a new content.

https://jira.ez.no/browse/EZS-14

**THINGS DONE**
* [x] Fetching content types from the system,
* [x] Filtering a list of content types with search query and selecting content type group.
* [x] Completed the code documentation,
* [x] Prepared JS unit tests,
* [x] Improved the visuals,
* [x] Create content view of PlatformUI

I think it's a bad idea to provide a route that will allow to create a new content. (In a typical web application you would do that in a POST request not in a GET request with some parameter in the query string) Instead, when you choose a content type in the list, this should create a new content/version and when that's done, the user should redirected to the `editContent` route.

From a technical point of view, the content/version creation + redirection should be done in a view service plugin (that for now is dedicated to the location view service)