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

> Premature optimization is the root of all evil

for now, please use the REST API and its client as much as possible, we'll work on performance afterwards.
And you are mixing field types and content types, here you are dealing with content types.