Selecting objects through viewport

[Qaomen]

Description
Currently, editor objects can only be selected in the sidebar menus. In more complex levels with many objects, it can be a chore to find the object you want to select. This feature aims to make the work flow more intuitive by allowing the user to select objects by clicking on them in the viewport.

Minimum Acceptance Criteria

• User should be able to select world objects by clicking them in the viewport.
• User should be able to select prefab entities by clicking them in the viewport.
• If a raycast doesn't hit any selectable objects, the current selected object should be deselected.

Optional Acceptance Criteria
Adding a highlight to objects the cursor hovers over could provide useful feedback for the user.
For prefab entity selection, it could be worth to add an indicator for which prefab is currently selected (based on the selected prefab entity).

Is blocked by the following issues
Though not technically blocking, the feature described in #151 helps with providing feedback to the user, and may be used for the optional acceptance criteria.