Maliput viewer

Nobody has claimed this yet.

### Bare bones

- [x] Create an empty 3D widget that uses 100% of the window.
- [x] Add support for reading command line parameters. Read a path from the command line that should point to the maliput file.
- [x] Given a path, load the road geometry in memory (this will require using maliput as a library). Focus on multilane for a starter.
- [x] Write the code that takes a road network pointer and returns a set of named meshes / layers.
- [x] Populate the 3D scene with the meshes.

**Key Result:** demonstrate the viewer, loading from the command line, a Maliput multilane format.

### Information labels (see maliput/maliput_viz#14)

- [ ] Set labels with the IDs for all the entities and no toggling can be done.
- [x] Provide the control box with different check boxes.
- [ ] Modify label duplication if necessary.
- [ ] Usability improvements.

**Key Result:** load a multilane road network and properly visualize text labels with relevant IDs.

### RoadGeometry properties (see issue maliput/delphyne_gui#113)

- [ ] After a click in the 3D widget over a road, get the 3D world coordinate from it in a text field.
- [ ] After a click in the 3D widget over a road, properly visualize coordinates and road metadata (eg lane ID).

**Key Result:** load a maliput multilane road netowork and get relevant information (eg. world and lane coordinates) after clicking on the road network.

### Load from widget and enable rendering options

- [ ] Add a UI button that opens a file dialog to choose the file to load. (Needs review)
- [ ] Add a set of checkboxes to show/hide different features.
- [ ] Add a button that allows to reloading current loaded file. (Needs review)

**Key Result:** load a maliput multilane from the widget and enable/disable rendering of features

### Simulation Functionality

- [ ] Establish a connection with the backend to receive the road network from it.
- [ ] Enable loading/rendering of a road network given a specification passed from the simulator.

**Key Result:** view/introspect road networks passed from the simulator.

Start by reviewing the existing 3D widget and the unchecked sections of this issue, along with the referenced maliput issues. No files or tests are named, so identify the relevant viewer entry points before starting. Done means the requested loading, labels, road metadata, rendering controls, and simulator integration work as described in each key result.

Written by the indexing model from the issue text.