Improve __repr__ for various objects

[sarlinpe]

Breaking changes:

• Sim3d.from_matrix becomes a constructor Sim3d(matrix)
• Camera.{model_id,model_name} are merged into Camera.model (via enum)
• Camera.params_info and Image.{num_points2D,num_points3D} become read-only properties (previously: functions)

Samples:

>> camera
Camera(camera_id=1, model=SIMPLE_RADIAL, width=780, height=1063, params=[1245.950053, 390.000000, 531.500000, 0.020831] (f, cx, cy, k))

>> print(rec.cameras[1].summary())
Camera:
    camera_id = 1
    model = CameraModelId.SIMPLE_RADIAL
    width = 780
    height = 1063
    focal_length = 1245.950052502772
    focal_length_x = 1245.950052502772
    focal_length_y = 1245.950052502772
    has_prior_focal_length = False
    principal_point_x = 390.0
    principal_point_y = 531.5
    params_info = f, cx, cy, k
    params = [1.24595005e+03 3.90000000e+02 5.31500000e+02 2.08308406e-02]

>> image
Image(image_id=1, camera_id=1, name="mapping/02928139_3448003521.jpg", triangulated=760/2313)

>> print(image.summary())
Image:
    image_id = 1
    camera_id = 1
    name = mapping/02928139_3448003521.jpg
    cam_from_world = Rigid3d(quat_xyzw=[0.0500042, 0.243753, -0.155877, 0.955922], t=[-1.37836, 0.000488448, -1.59398])
    cam_from_world_prior = Rigid3d(quat_xyzw=[nan, nan, nan, nan], t=[nan, nan, nan])
    points2D = [ ... 2313 elements ... ]
    registered = True
    num_points2D = 2313
    num_points3D = 760
    num_observations = 0
    num_correspondences = 0

>> sim3d
Sim3d(scale=1, quat_xyzw=[0, 0, 0, 1], t=[0, 0, 0])